PDA

View Full Version : Optimized Suppressed Upper build



mtdawg169
2 February 2016, 13:33
Hello gents, I've been a member here for a good while, but never very active on WEVO. I'm looking to change that, so I thought I'd kick it off with a new build thread. I initially posted this on a local forum where the average member is less technically savvy than the average WEVO member, so please forgive any parts that may seem rudimentary.

These days, there are all sorts of products and gadgets out there to help deal with shooting suppressed (technically over gassing). Adjustable gas blocks ("AGB"), adjustable carriers, the WAR upper, even adjustable gas keys to replace the standard versions. The primary reason we have seen the introduction of these products is because the introduction of a suppressor increases gas flow and overall pressure within the system. This increased pressure can cause functional issues & excess gas ejected from the receiver.

To me, none of these solutions are really ideal. (blasphemy, I know) Most of them involve the addition of small set screws, detents, etc that quite frankly, I just don't trust. Sure, they work. But I'd just prefer a more simplistic solution. Adjustable carriers and gas keys came along as a drop in solution for folks that didn't want to screw around with the gas block. Or feasibly, something you could install and adjust without disassembling the upper.

Adjustable parts exist primarily for one reason. Too damn many companies are producing barrels with huge gas ports. That's fine if you're shooting unsuppressed and like to shoot weak steel case ammo. However, introduce full power ammo and a suppressor and you may have functional issues from over gassing or the dreaded "gas face".

Regarding the use of adjustable parts, one of the things I've always felt was that while they work, reducing gas flow at a location other than the gas port, was not ideal. It works, but realistically, all we're doing is putting a band aid on the real issue - a hogged out GP.

What do I mean by oversized? Well, when I run something like my BCM or KAC uppers with a suppressor, they are reliable, gas isn't too terrible and recoil impulse is smooth. Comparatively, alot of guns would require a heavier buffer to achieve the same feel and would still dump a lot of gas in your face. My buddy's MK18 will choke you out with his specwar attached. While DD makes a fine weapon, the commercial version of the MK18 uses a larger port than the one they build for the military. Why? So people don't complain that it won't run weak ammo. Downside? Harsh recoil and tons of gas with a suppressor attached.

So what's the best solution for someone who wants to shoot suppressed, most if not all of the time? The better solution is ultimately, a smaller gas port, reducing the gas flow at the source. Problem? No one offers them specifically sized for suppressor use, ever. I've known a few guys that had connections with companies like Noveske that were able to custom order a barrel for this purpose and spec out their own gas port size. But for the masses, it just hasn't been an option. Most manufacturers don't want to bother with them because the market for a reduced gas port ("RGP") barrel is fairly narrow. It's not for your average shooter.

Well, Sionics Weapon Systems in AZ is now offering a reduced gas port barrel in limited numbers. SIONICS has just released what I've been wanting for a long time. An 11.5 reduced gas port barrel, that is quality made throughout. It's currently on pre-order, so I should have it in a few weeks. And it is designed primarily for suppressed use. Per Sionics, it's for "suppressed use only" but set up correctly, can be used reliably without the suppressor too. This means, the gas port has been sized on the ragged edge of small. And that's a good thing for me. It's small enough to work reliably, but not so small that it can't serve double duty.
Pros: reduced gas and recoil.
Cons: possible ammo sensitivity during unsuppressed use.

https://uploads.tapatalk-cdn.com/20160110/dcc42afbd6973d82a831fd76baeca6f2.jpg

http://sionicsweaponsystems.com/store2015/5/61-5-chrome-lined-stripped.html

Barrel specs:
These Barrels are designed for use with a suppressor. We do not recommend using them without a suppressor as the weapon may not cycle properly.

These will be Limited production runs and only a handful will be available at a time. Availability will be intermittent.

SIONICS Barrels are manufactured from CMV 4150 Ordnance Steel. All Barrels are Radiograph and MPI tested.

Features:

11595E CMV 4150 Steel
M4 Barrel Extension
5.56mm NATO Chamber
1/7 Twist Rate
.750 Gas Block
Chrome Lined Chamber and Bore
SIONICS Designed Medium Contour
Manganese Phosphate Finish
Standard 1/2X28 Muzzle Threading
Carbine Gas System
X-Rayed and MP Inspected
Barrel Weight - 1 lb. 7 oz.

Build plans
Sionics 11.5 RGP barrel
BCM4 upper receiver
BCM KMR-A rail - 10"
LMT enhanced carrier (Gen 4)
BCM bolt
Standard BCM gas block
Upper will be mounted on a lower already equipped with a Vltor A5 buffer system.

I'm already very acquainted with the LMT enhanced carrier and Vltor A5 buffer system. Both are well proven additions, especially for suppressed use. My goals for this build are as follows:

Reduced weight vs my current 11.5 upper
Reliable function with / without suppressor
No adjustment or buffer swaps necessary
Minimal recoil / smooth impulse
Less gas face

Will it be the ultimate suppressed upper build? I guess we'll see. But I'm looking forward to it in a big way.

A little more info from Sionics Master Armorer.


Just to add some additional information to this. The first batch of barrels was done for a specific client (local SWAT) that wanted to replace their ‹ber-heavy 11.5" piston guns. The goal was to trim weight, reduce gassing and maintain reliability with their duty ammo. They also stated that these would only be used with suppressors and the likelihood of shooting without one was very slim. However, we wanted to ensure that they would run un-suppressed in an emergency.


Once we had the basics down we then used a variety of port sizes and conducted testing with several types of ammo and buffer combinations. The end result was a suppressed SBR that would cycle and function with a wide variety of ammunition, and utilize standard components (no adjustable gas block).

mtdawg169
2 February 2016, 13:35
Build list:

BCM4 upper receiver
BCM KMR Alpha - 10"
BCM gas block and tube
Sionics RGP 11.5 barrel

Already on hand:

LMT enhanced carrier
BCM bolt, cam pin, firing pin, etc
BCM Gunfighter charging handle
Magpul MBUS Pro sights
Aimpoint T1 w/ Bobro mount
BCM KAG
Surefire Mini Scout on a KAC keymod mount

All riding on a Form 1 BCM lower with Geissele SSA trigger and Vltor A5 buffer system. This thing is going to be sweet.

Just one thing missing...
http://uploads.tapatalk-cdn.com/20160201/073dfa85bac668152fe4cc8597c22663.jpg

Silencer Shop
2 February 2016, 13:52
Very interesting. Keep us updated as you progress on this.

mtdawg169
2 February 2016, 15:26
Will do. The barrels should be finished soon, so I'll update once I get it together and again after I get it to the range.

DutyUse
2 February 2016, 19:34
Should make for a nice host. I've been piecing together an almost identical build, been on the fence about the sionics barrel though

mtdawg169
2 February 2016, 19:37
Should make for a nice host. I've been piecing together an almost identical build, been on the fence about the sionics barrel though
What barrel are you considering?

My current 11.5 upper is a KAC SR16 barreled upper (Christmas Cheer barrel) with a URX 3.1. It's a bit heavy and I've been thinking about putting together a lighter upper for a while. The Sionics barrel offering was enough to push me over the edge and set one up with a KMR-A.

DutyUse
2 February 2016, 19:43
What barrel are you considering?

My current 11.5 upper is a KAC SR16 barreled upper (Christmas Cheer barrel) with a URX 3.1. It's a bit heavy and I've been thinking about putting together a lighter upper for a while. The Sionics barrel offering was enough to push me over the edge and set one up with a KMR-A.

http://images.tapatalk-cdn.com/16/02/02/7a9fbcb335b0ffb10d87daa5c8738cca.jpg

Planned on using this BCM 11.5 bfh barrel that's been kicking around with 10" kmr and BCM upper. I've had it for ages but I knew it would be a suppressed only upper so I've been researching how to cut down on the gas

mtdawg169
2 February 2016, 19:50
http://images.tapatalk-cdn.com/16/02/02/7a9fbcb335b0ffb10d87daa5c8738cca.jpg

Planned on using this BCM 11.5 bfh barrel that's been kicking around with 10" kmr and BCM upper. I've had it for ages but I knew it would be a suppressed only upper so I've been researching how to cut down on the gas
I was seriously considering using their ELW barrel initially. Have you given any thought to using the Black River Tactical inserts?

ETA: not cool, sneaking those Fathom Spade carriers into the background!

DutyUse
2 February 2016, 19:59
I was seriously considering using their ELW barrel initially. Have you given any thought to using the Black River Tactical inserts?

Honestly I hadn't considered it. How permeant is the modification? A suppresser friendly upper like the Noveske switchblock has been more and more appealing to me lately

mtdawg169
2 February 2016, 20:11
Honestly I hadn't considered it. How permeant is the modification? A suppresser friendly upper like the Noveske switchblock has been more and more appealing to me lately
It's basically a set screw with a precision port. Available in numerous sizes. I think each set includes a range of three sizes. You just thread the inside of the gas block, screw in the insert and reinstall. Clint at BRT can help you decide on the appropriate sizes before you order. I think he even offers a pinable GB with the inserts for $55. You just try the different sizes until you find the one that works best. Once you've settled on the appropriate size, you never touch it again. Obviously, some experimentation is involved on the front end, but once it's done, you just roll on. If you ever want to take it out, just pull the block and remove it.

Pic from BRT website
http://uploads.tapatalk-cdn.com/20160203/320411f16f018704c0efa3d09b805c84.jpg

http://www.blackrivertactical.com/concrete5/customtune-gas-port/

DutyUse
2 February 2016, 20:15
Thanks for posting brother, I really appreciate the write up and knowledge. It sounds pretty cool, but I think just putting the BCM barrel back in the safe and getting a sionics rgp barrel might be the way to go on this one

mtdawg169
2 February 2016, 20:18
Thanks for posting brother, I really appreciate the write up and knowledge. It sounds pretty cool, but I think just putting the BCM barrel back in the safe and getting a sionics rgp barrel might be the way to go on this one
That was my thinking. The port isn't stupid small though. I believe it's around 0.070. But don't quote me on that. It will still run without a suppressor. But I suspect it may be a bit ammo sensitive. When I get mine set up, I'll be running some different ammo through it to see where the limits are.

mtdawg169
2 February 2016, 20:22
This thread probably sounds like an advertisement. For the record, I'm not affiliated with BRT, Sionics or any other company. And I do not work in the industry in any capacity.

alamo5000
2 February 2016, 20:26
I read the initial post but not all the replies yet...

Since I have gotten a suppressor and have been shooting it on various things I have learned a few things.

Long story short I don't know if simply changing the port sizing is going to have the benefits you are after. It's sheer physics.

As others know I am pretty frickin' nerdy on a lot of things...

I am not trying to rain on any parades but I will explain why I think what I think. Maybe it will help with your process, maybe not.

Your ammo creates the most important factor which is PSI. The actual PSI (not CUP or anything else) will be the best measurement to use. PSI is what propels your bullet forward... and backpressure from a can on the barrel happens primarily in your bore, not your gas tube. Shorter barrels have a substantially greater PSI at the bullet exit hence a much louder 'boom' ...as the guys at Griffin put it, 'you decork' at a much higher PSI... whereas with a longer barrel those gasses are almost spent and hence the suppressor can more efficiently handle that decorking of that gas better. 11.5" inches is a whole different animal than say 18" inches... the total inner volume of the bore of each is substantially different.

The whole gas in the face thing is again not caused by porting of the barrel. It's caused by gas being trapped under extreme pressures in small containers, IE the bore of the gun....basically if you don't want gas in your face use a longer barrel and/or a more efficient suppressor that will help dissipate those gases more. To be 'perfect' the suppressor would probably have to be physically bigger IE have a bigger volume and a means to manage those gases.

When you shoot suppressed look at your spent cases, your mags, and your upper and lower... all that carbon comes from the back pressures in the bore itself, not from the gas tube depositing it backwards...if you look at the proportional size of a gas port to a .224 size bore there is no comparison... gas will take the path of least resistance.

Although this post was originally intended to be about noise it also applies to pressure and back pressure too... take a look at one of my old threads so you can see what I mean...

http://www.weaponevolution.com/forum/showthread.php?8747-SBR-Noise&highlight=

On a 10.5 barrel you have about 11,500 PSI at bullet exit... on a 16" barrel it's already down to just over 7,000 PSI... there is just simply more volume to deal with...

Also the nature of the gas has changed too. On a short barrel the gas is still in explosive expansion stage and on a longer barrel the gas has already expended a lot more of it's energy...

Hence this overall picture kind of tells the story (at least to me)...that the shorter the barrel the higher the pressure. The longer the barrel the less the pressure. One will have more gas in the face because of that bore pressure and one will have less gas in the face because of the same thing.

DutyUse
2 February 2016, 20:27
I really wish they made the same barrel but in 10.3" for a shorter overall package.

As much business as I've given Noveske I should try and call them and see if they would cut me a custom gas port

alamo5000
2 February 2016, 20:45
I will also add that adjustable gas blocks DO make a difference at least to me... the MORE they are opened up they do release pressure but this has to be balanced out with functionality of the gun itself. If the gun won't cycle I mean what difference does it make?

On two different guns... both with identical adjustable gas blocks there are two entirely different settings that must be used to have good functionality even with all other things being equal... same ammo same everything... but those differences though are due to barrel length more than anything....

As of right now I have my gas blocks set to where the gun will cycle with or without a suppressor. I did have them tuned to where it would lock the bolt back when suppressed but not unsuppressed and I decided I didn't like that. The differences are minor from one extra click.

With a longer barrel (16 or 18 on up) I have never gotten gas in my face at least not with my set up. The shorter you go though it's just going to happen to some degree or another.

mtdawg169
2 February 2016, 20:47
I read the initial post but not all the replies yet...

Since I have gotten a suppressor and have been shooting it on various things I have learned a few things.

Long story short I don't know if simply changing the port sizing is going to have the benefits you are after. It's sheer physics.

As others know I am pretty frickin' nerdy on a lot of things...

I am not trying to rain on any parades but I will explain why I think what I think. Maybe it will help with your process, maybe not.

Your ammo creates the most important factor which is PSI. The actual PSI (not CUP or anything else) will be the best measurement to use. PSI is what propels your bullet forward... and backpressure from a can on the barrel happens primarily in your bore, not your gas tube. Shorter barrels have a substantially greater PSI at the bullet exit hence a much louder 'boom' ...as the guys at Griffin put it, 'you decork' at a much higher PSI... whereas with a longer barrel those gasses are almost spent and hence the suppressor can more efficiently handle that decorking of that gas better. 11.5" inches is a whole different animal than say 18" inches... the total inner volume of the bore of each is substantially different.

The whole gas in the face thing is again not caused by porting of the barrel. It's caused by gas being trapped under extreme pressures in small containers, IE the bore of the gun....basically if you don't want gas in your face use a longer barrel and/or a more efficient suppressor that will help dissipate those gases more. To be 'perfect' the suppressor would probably have to be physically bigger IE have a bigger volume and a means to manage those gases.

When you shoot suppressed look at your spent cases, your mags, and your upper and lower... all that carbon comes from the back pressures in the bore itself, not from the gas tube depositing it backwards...if you look at the proportional size of a gas port to a .224 size bore there is no comparison... gas will take the path of least resistance.

Although this post was originally intended to be about noise it also applies to pressure and back pressure too... take a look at one of my old threads so you can see what I mean...

http://www.weaponevolution.com/forum/showthread.php?8747-SBR-Noise&highlight=

On a 10.5 barrel you have about 11,500 PSI at bullet exit... on a 16" barrel it's already down to just over 7,000 PSI... there is just simply more volume to deal with...

Also the nature of the gas has changed too. On a short barrel the gas is still in explosive expansion stage and on a longer barrel the gas has already expended a lot more of it's energy...

Hence this overall picture kind of tells the story (at least to me)...that the shorter the barrel the higher the pressure. The longer the barrel the less the pressure. One will have more gas in the face because of that bore pressure and one will have less gas in the face because of the same thing.
Yeah, sorry about the length of the OP. I'd have to say that in theory, I understand what you're saying. But in practice, I've had a wholly different experience. Any suppressed gun is going to run dirty, we all get that. Especially SBRs. Just comes with the territory. But over the last couple of years shooting almost exclusively with a suppressor, I've found that port size does make a difference. Not only in reliability and recoil impulse, but also in the amount of excess gas experienced by the shooter. For example, shooting my current 11.5 versus my buddy's Mk18 are two totally different experiences. The MK18 is way overgassed. And it dumps much more gas out of the receiver.

But, the barrel and port are only part of the equation. And dealing with excess gas is only one of the goals. The other pieces of the puzzle here are the LMT enhanced carrier and the Vltor A5. Both of these will delay unlocking, which increases that "uncorking" time. The e-carrier also helps redirect some of that gas. As I mentioned, dealing with excess gas is only one goal. And you can never really eliminate it altogether. The other goals here are to reduce weight, produce a smooth recoil impulse and maintain simplicity. Hence, the reduced port vs an AGB. This will allow me to just run a standard GB. And not have to employ other parts that require a switch or set screw adjustment, like the gemtech carrier or adjustable gas key.

Ultimately, I want to set it up so I can shoot with or without a suppressor and not have to flip a switch, pull a carrier out, etc. Just slap on a can and go. It's still a compromise of sorts though. An AGB would allow even more fine tuning. But I don't want to add any potential failure points to the gun.

mtdawg169
2 February 2016, 20:54
I really wish they made the same barrel but in 10.3" for a shorter overall package.

As much business as I've given Noveske I should try and call them and see if they would cut me a custom gas port
BCM is never going to make a 10.x.

I believe Noveske has done custom ports for others in the past. But who knows these days.

Farva
2 February 2016, 21:19
I'll be using a BCM 11.5" ELW Fluted barrel for my suppressed upper as well

Farva
2 February 2016, 22:00
I'll be using a BCM 11.5" ELW Fluted barrel for my suppressed upper as well

BC98
3 February 2016, 12:10
OP,

I'm very interested in how your build turns out and functions. I've got a barrel in one of my SBR's that has what I would consider an abnormally small (.065") port on a 12.5" barrel. I shot it with a friends suppressor and the recoil felt good (less than a different upper with a larger port) and gas in the face was still there but not bad. I've toyed with the idea of picking up one of the Baby Govnah blocks from MicroMOA and drill the port to cycle with the can (but not without). The blocks are cheap and wouldn't be too hard to swap around.

Very cool.

BC98
4 February 2016, 12:07
I was thinking about this build concept last night and had a counter-hypothesis to alamo's post. (Bit long-winded so bear with me...)

If a barreled upper and reciprocating assembly (including buffer and spring) are looked at as a system, then we can look at gas volume management. For a given bolt carrier/buffer/spring set up in an unsuppressed upper, a certain volume of gas (call it gas drive, maybe?) is required to unlock the bolt. In an ideal situation, the gas port is sized to provide only the gas drive necessary to cycle the action during the dwell time of the bullet (i.e. when the bullet is between the gas port and the muzzle during its travel down the bore). When the bullet leaves the muzzle, system pressure drops to zero and gas drive is removed. The momentum of the bolt carrier then completes the extraction and feed cycle as the spring and buffer do its work. If the system is balanced, there will be a minimum amount of pressure present in the bore that will push carbon and fouling back into the upper through the bore and chamber.

In an unsuppressed upper, adding a can essentially artificially increases the dwell time of the bullet. Pressure should decrease in the system when the bullet transitions from the bore into the suppressor but the suppressor is still a partially closed system that does not allow the gas drive to totally dissipate. Since pressure and the gas drive are still present, you should still see some remaining pressure pushing carbon and fouling into the upper after the case extraction has started.

Now, if you are able to reduce the gas port diameter then it may be possible to correct this situation for a suppressed system. Reducing GP diameter should delay the time for the necessary gas drive to be reached to start unlocking the bolt and the onset of the extraction cycle. Essentially, the idea would be to keep the chamber sealed longer to keep all of that residual pressure when the bullet is resident in the suppressor from pushing carbon and fouling back into the chamber/upper. I believe this is why stronger buffer springs, heavier buffers, and enhanced carriers can be used to somewhat delay the onset of bolt unlock. Another likely advantage is that gas to the face SHOULD be reduced.

There are downsides to this approach. As youíve effectively narrowed your range of operation, the upper will likely not cycle without a can. Any parts changes (such as buffers, springs, enhanced bolt carriers, or even suppressor), would likely change the required gas drive for correct operation and possibly lead to an increase in fouling, gas blowback, and/or felt recoil. Depending on the final GP diameter, the system may also have some ammo sensitivity in function.

I have no clue if Iím way out in left field but this seems to makes sense to me. Admittedly, this would be a VERY narrow use application but I may likely try it down the road.

John Moses
4 February 2016, 13:16
C4Grant was on another forum often with dedicated Suppressed builds with custom gas ports, and tuned barrel lengths to get the unlock, dwell etc exactly perfect. I wonder if he is around or on this board. He is a wealth of information. I think his shop was G&R or something like that. I have the rubber city adjustable gas key on the way, but Brownells shipping is like a slow boat from China.

Joelski
4 February 2016, 14:10
This is why I went with 300 BLK. All this figuring madness makes my head hurt. Great passtime for an OCD though.

Question for Nerds/Physics Geeks: Is there an absolute pressure for a given orifice size? Assuming variations in combusted gas density and temperature are negligible (Variations in loads would be exempt, as you can tune the pressure to some extent), would reducing gas port size at some point hamper the efficiency of the system? I'm thinking a constricted gas port would produce kind of a hydraulics/friction loss type thing, maybe. Wouldn't it be better to take the gas port out of the problem by using an adjustable gas block? That's effed up! Therefore, God created 300 BLK for us non-calculus/physics people!

BC98
4 February 2016, 14:29
This is why I went with 300 BLK. All this figuring madness makes my head hurt. Great passtime for an OCD though.

Question for Nerds/Physics Geeks: Is there an absolute pressure for a given orifice size? Assuming variations in combusted gas density and temperature are negligible (Variations in loads would be exempt, as you can tune the pressure to some extent), would reducing gas port size at some point hamper the efficiency of the system? I'm thinking a constricted gas port would produce kind of a hydraulics/friction loss type thing, maybe. Wouldn't it be better to take the gas port out of the problem by using an adjustable gas block? That's effed up! Therefore, God created 300 BLK for us non-calculus/physics people!

If you want the flexibility to shoot both suppressed and unsuppressed the AGB makes more sense. If you're only going to shoot suppressed and don't care about unsuppressed function, having a dedicated gas port would be preferable as it reduces cost (assuming the barrel doesn't have to be an expensive custom build) and complexity. Another option for dedicated suppressed would be a gas block that allows you to drill your own port size.

alamo5000
4 February 2016, 15:34
All this figuring madness makes my head hurt. Great passtime for an OCD though.


Say what?!

http://treasure.diylol.com/uploads/post/image/417643/resized_robert-de-niro-meme-generator-are-you-talking-to-me-fb7b4e.jpg

[:D][:D][:D]

alamo5000
4 February 2016, 16:30
This is why I went with 300 BLK. All this figuring madness makes my head hurt. Great passtime for an OCD though.

Question for Nerds/Physics Geeks: Is there an absolute pressure for a given orifice size? Assuming variations in combusted gas density and temperature are negligible (Variations in loads would be exempt, as you can tune the pressure to some extent), would reducing gas port size at some point hamper the efficiency of the system? I'm thinking a constricted gas port would produce kind of a hydraulics/friction loss type thing, maybe. Wouldn't it be better to take the gas port out of the problem by using an adjustable gas block? That's effed up! Therefore, God created 300 BLK for us non-calculus/physics people!

My opinion on how to 'solve the problem' would be a whole lot more simple and have better results...

I would think using a reflex suppressor with greater internal volume would help a whole lot more with gas in the face than trying to mess with port sizes. That said I am new and I frequent Holiday Inn Express so don't take me too seriously. I am just thinking out loud. Less than a year ago I didn't even own a suppressor so I am far from an expert. I am hoping someone will correct me and teach me so don't think of my posts as being 'an expert'... (I'm not)...I just have a nerd gene that needs to be itched from time to time [BD]

As for your question what do you mean 'absolute pressure'? In my opinion there is never an 'absolute pressure' when it comes to shooting. The pressure in the chamber will be different than the pressure 3 inches down the bore and different again 6 inches and 12 inches and so on and so forth. Just think fire hose. If you are standing at point blank and they blast you with a fire hose it can knock you down. Then step back 20 feet and try the same experiment...the pressure won't be equal the farther out you go...

I have done a little bit of looking and here is what I have found out (for my own use and curiosity). Powders burn at all different rates and they all create pressure but the 'signature' of that type of pressure will vary. With some fast powders you have a quick 'burn bang' so the pressure spikes quickly then falls off fast simply because there isn't a more sustained expansion of powder... you also have slower powders that will offer more of a sustained push to the projectile. There is a whole spectrum there that can be optimized for a barrel length. That said ALL of them will generate PSI. Without it there won't be forward motion.

Long story short those gasses all expand and spend their energy in a confined space but generally in a forward momentum. If there is no pressure (PSI) then the bullet won't be propelled forward...

The whole point of a gas port is to make the gun cycle, in my case in a semi auto fashion. It will shoot just fine with NO gas port even in an AR platform... you will though just have a single shot rifle that needs to recharge manually every time. The forward momentum of the bullet won't have enough pressure on it's own to blow the BCG backwards... hence some of that energy going forward is harnessed and blown through the tube so that your gun will cycle. The whole point of the gas port is to have a rifle that will recharge itself. By using adjustable gas blocks that are open too much or fiddling with the porting can result in too much or too little gas going through the gas tube. I can make my AR a single shot with NO problem. Just open up that adjustable block and bleed off too much gas and it won't cycle.

Constricting the port size though can have various consequences that I don't fully know what the result would be... but I figure constrict it too much and it won't function the same way as if you bleed off too much gas with an adjustable block.

My assertion is though that the primary 'gas in the face' isn't caused by gas through the gas tube at all. The barrel is full of of 'gasses' even if they are stationary before a shot is taken... and when you pull the trigger the bullet has to push all that out of the way while having a huge amount of PSI behind the bullet. But when you add a suppressor it makes it harder because there is increased resistance going forward so some of the hot expanding gasses escape backwards...They just take the path of least resistance. So in essence the gas generated from the 'bang' is pushing forward and backward both in a linear fashion in both directions. It might be 95% forward and 5% back...for normal shooting and you won't even notice that 5%...but if you increase the resistance it makes that back number go up to say 10 or 15% which is when you experience gas in the face...

EDIT: I would also add that when the bullet actually leaves the barrel and those hot gasses hit the wide open... they can dissipate on their own...but they make a big boom when this happens... Add a suppressor and those gasses can't just freely go where they want after they are released... which adds to the whole 'resistance' thing...so it's pushing gas backwards...

mtdawg169
4 February 2016, 20:16
I was thinking about this build concept last night and had a counter-hypothesis to alamo's post. (Bit long-winded so bear with me...)

If a barreled upper and reciprocating assembly (including buffer and spring) are looked at as a system, then we can look at gas volume management. For a given bolt carrier/buffer/spring set up in an unsuppressed upper, a certain volume of gas (call it gas drive, maybe?) is required to unlock the bolt. In an ideal situation, the gas port is sized to provide only the gas drive necessary to cycle the action during the dwell time of the bullet (i.e. when the bullet is between the gas port and the muzzle during its travel down the bore). When the bullet leaves the muzzle, system pressure drops to zero and gas drive is removed. The momentum of the bolt carrier then completes the extraction and feed cycle as the spring and buffer do its work. If the system is balanced, there will be a minimum amount of pressure present in the bore that will push carbon and fouling back into the upper through the bore and chamber.

In an unsuppressed upper, adding a can essentially artificially increases the dwell time of the bullet. Pressure should decrease in the system when the bullet transitions from the bore into the suppressor but the suppressor is still a partially closed system that does not allow the gas drive to totally dissipate. Since pressure and the gas drive are still present, you should still see some remaining pressure pushing carbon and fouling into the upper after the case extraction has started.

Now, if you are able to reduce the gas port diameter then it may be possible to correct this situation for a suppressed system. Reducing GP diameter should delay the time for the necessary gas drive to be reached to start unlocking the bolt and the onset of the extraction cycle. Essentially, the idea would be to keep the chamber sealed longer to keep all of that residual pressure when the bullet is resident in the suppressor from pushing carbon and fouling back into the chamber/upper. I believe this is why stronger buffer springs, heavier buffers, and enhanced carriers can be used to somewhat delay the onset of bolt unlock. Another likely advantage is that gas to the face SHOULD be reduced.

There are downsides to this approach. As youíve effectively narrowed your range of operation, the upper will likely not cycle without a can. Any parts changes (such as buffers, springs, enhanced bolt carriers, or even suppressor), would likely change the required gas drive for correct operation and possibly lead to an increase in fouling, gas blowback, and/or felt recoil. Depending on the final GP diameter, the system may also have some ammo sensitivity in function.

I have no clue if Iím way out in left field but this seems to makes sense to me. Admittedly, this would be a VERY narrow use application but I may likely try it down the road.
Sorry guys, it's been a long day. Thanks for the input, there are some great points being made here.

@BC98 You're pretty much on track with my theory behind this build. The use of the LMT carrier and Vltor A5 buffer system both work to delay unlocking. Hence, they will allow pressures to drop and increase reliable extraction. I'm theorizing a bit, but I also believe that will help to some degree on blowback as well.

mtdawg169
4 February 2016, 20:23
C4Grant was on another forum often with dedicated Suppressed builds with custom gas ports, and tuned barrel lengths to get the unlock, dwell etc exactly perfect. I wonder if he is around or on this board. He is a wealth of information. I think his shop was G&R or something like that. I have the rubber city adjustable gas key on the way, but Brownells shipping is like a slow boat from China.
Grant's thread from several years ago is what initially turned me on to this idea. My build will be pretty similar, except that I don't want to use an adjustable gas block, adjustable carrier key, WAR upper or gemtech type carrier.

The reasons are simple. I don't want to introduce any adjustable parts to the gun. First, because I don't want to present any additional potential mechanical failure points to the system. And second, I don't want to have to make adjustments, pull the gun apart to flip a switch on the carrier or any other "changes" to switch from unsuppressed to suppressed shooting.

mtdawg169
4 February 2016, 20:25
If you want the flexibility to shoot both suppressed and unsuppressed the AGB makes more sense. If you're only going to shoot suppressed and don't care about unsuppressed function, having a dedicated gas port would be preferable as it reduces cost (assuming the barrel doesn't have to be an expensive custom build) and complexity. Another option for dedicated suppressed would be a gas block that allows you to drill your own port size.
I'm forfeiting some ability to further refine gas drive with an AGB. That's a compromise I'm willing to make in order to meet the other stated goals for the build.

mtdawg169
4 February 2016, 20:34
My opinion on how to 'solve the problem' would be a whole lot more simple and have better results...

I would think using a reflex suppressor with greater internal volume would help a whole lot more with gas in the face than trying to mess with port sizes. That said I am new and I frequent Holiday Inn Express so don't take me too seriously. I am just thinking out loud. Less than a year ago I didn't even own a suppressor so I am far from an expert. I am hoping someone will correct me and teach me so don't think of my posts as being 'an expert'... (I'm not)...I just have a nerd gene that needs to be itched from time to time [BD]

As for your question what do you mean 'absolute pressure'? In my opinion there is never an 'absolute pressure' when it comes to shooting. The pressure in the chamber will be different than the pressure 3 inches down the bore and different again 6 inches and 12 inches and so on and so forth. Just think fire hose. If you are standing at point blank and they blast you with a fire hose it can knock you down. Then step back 20 feet and try the same experiment...the pressure won't be equal the farther out you go...

I have done a little bit of looking and here is what I have found out (for my own use and curiosity). Powders burn at all different rates and they all create pressure but the 'signature' of that type of pressure will vary. With some fast powders you have a quick 'burn bang' so the pressure spikes quickly then falls off fast simply because there isn't a more sustained expansion of powder... you also have slower powders that will offer more of a sustained push to the projectile. There is a whole spectrum there that can be optimized for a barrel length. That said ALL of them will generate PSI. Without it there won't be forward motion.

Long story short those gasses all expand and spend their energy in a confined space but generally in a forward momentum. If there is no pressure (PSI) then the bullet won't be propelled forward...

The whole point of a gas port is to make the gun cycle, in my case in a semi auto fashion. It will shoot just fine with NO gas port even in an AR platform... you will though just have a single shot rifle that needs to recharge manually every time. The forward momentum of the bullet won't have enough pressure on it's own to blow the BCG backwards... hence some of that energy going forward is harnessed and blown through the tube so that your gun will cycle. The whole point of the gas port is to have a rifle that will recharge itself. By using adjustable gas blocks that are open too much or fiddling with the porting can result in too much or too little gas going through the gas tube. I can make my AR a single shot with NO problem. Just open up that adjustable block and bleed off too much gas and it won't cycle.

Constricting the port size though can have various consequences that I don't fully know what the result would be... but I figure constrict it too much and it won't function the same way as if you bleed off too much gas with an adjustable block.

My assertion is though that the primary 'gas in the face' isn't caused by gas through the gas tube at all. The barrel is full of of 'gasses' even if they are stationary before a shot is taken... and when you pull the trigger the bullet has to push all that out of the way while having a huge amount of PSI behind the bullet. But when you add a suppressor it makes it harder because there is increased resistance going forward so some of the hot expanding gasses escape backwards...They just take the path of least resistance. So in essence the gas generated from the 'bang' is pushing forward and backward both in a linear fashion in both directions. It might be 95% forward and 5% back...for normal shooting and you won't even notice that 5%...but if you increase the resistance it makes that back number go up to say 10 or 15% which is when you experience gas in the face...

EDIT: I would also add that when the bullet actually leaves the barrel and those hot gasses hit the wide open... they can dissipate on their own...but they make a big boom when this happens... Add a suppressor and those gasses can't just freely go where they want after they are released... which adds to the whole 'resistance' thing...so it's pushing gas backwards...
Quite a bit of excess gas is expelled from the chamber. Just examine a case fired from a suppressed gun vs unsuppressed. There's no getting away from that with a suppressor. However, I have seen a noticeable difference in how much gas you have to deal with depending on port sizes. Eliminating excess gas in a suppressed SBR isn't going to happen completely. But if I can reduce it to some degree, I'll be happy. And if it doesn't produce any change, I'll still be happy. Why? Because I'm trying to accomplish several things here, including weight reduction vs my current 11.5 upper and produce a nice smooth recoil impulse. These two items, I have no doubt I'll achieve.

mtdawg169
31 March 2016, 21:19
It's alive!

http://uploads.tapatalk-cdn.com/20160401/bf0138e70b2f7f4699584b37a242f968.jpghttp://uploads.tapatalk-cdn.com/20160401/369019c077893feeb3f3938ad2debe44.jpghttp://uploads.tapatalk-cdn.com/20160401/f50f91cc424b65930ea45cd5a4c3f8d9.jpghttp://uploads.tapatalk-cdn.com/20160401/ce695ac0a1bf66dd7e2e03caca93efa8.jpghttp://uploads.tapatalk-cdn.com/20160401/7bdc4d1d6da7dbe4156534706d9f6cc6.jpg

usbp379
17 October 2016, 02:11
Bump for updates.

Sent from my GT-P3113 using Tapatalk

mtdawg169
17 October 2016, 03:47
Well, she runs like a raped ape. I ended up with an A5H3 buffer and Springco Green action spring in her, along with the LMT enhanced carrier. The gun is running exceptionally well and has become my favorite upper, by far.

Here it is, suppressed full auto, just for fun. Magpul D60.
https://youtu.be/auox8hfNECA

Sent from my SM-G920V using Tapatalk

mtdawg169
17 October 2016, 05:25
Bump for updates.

Sent from my GT-P3113 using Tapatalk
Is there any specific information you're interested in?

usbp379
17 October 2016, 17:10
Just curious. Thanks for the update.

Sent from my GT-P3113 using Tapatalk

mtdawg169
17 October 2016, 17:26
Just curious. Thanks for the update.

Sent from my GT-P3113 using Tapatalk
It has been extremely reliable thus far. It honestly has more recoil impulse with the suppressor attached than it does unsuppressed. The gas blowback is better than my buddies Mk18, a noveske N4 upper and a PSA 10.5. BUT blowback is not totally eliminated. I don't think that's possible with a suppressed SBR. The best you can hope for is to reduce it. The biggest difference I can see is that gas coming from the charging handle area is minimized and the majority is coming from the ejection port.