Adjustable Gas Block Questions

[alamo5000]

Today I got my adjustable gas block in. I bought the Sentry 7 from SLR...

http://slrrifleworks.com/image/cache/data/sentry-7s-gas-block-600x600.jpg

I already took the old one off, and installed the new one. It's ready to go. The hardest part of the thing was removing the old roll pin and then removing the gas tube from the old gas block. Man, that sucker was in there! But I got it all put together in no time flat.

I would like to hear some ideas or opinions... so do or can adjustable gas blocks effect the accuracy of a non suppressed rifle? In theory could you tune your gas and somehow alter velocity to some degree? Or is the velocity pretty much already set since there is 10 or 11 inches of barrel before you get to the block? It seems like there would have to be some major bleed off to alter the projectile any, but I don't know that for sure.

My thinking is that the block regulates the gas that blows back your BCG so if you bleed it off too much (I am talking unsupressed) it could cause short strokes or whatnot. (I had this experience with the T&E upper where the bolt would not lock back.)

The main reason I got it was in anticipation of my suppressor. Of course I get it... the suppressor traps gasses and can cause a lot more gas than normal to blow back your bolt. Hence the regulation.

Now that I have it installed and ready what is the optimal performance for the gun with that on there? What should I be looking for? What is the 'correct' ejection pattern for my brass? The rifle worked just fine with a standard block so in theory I could just open it wide open and be back to where I started (until my suppressor gets here)...

Also when the suppressor does get here what kind of stuff should I look out for when adjusting it? Anything that could possibly harm my suppressor or my gun? What process do you use to dial it in and how do you know that it's 'right'?

And I guess lastly, after I shoot a while do I ever need to clean the thing?

[Former11B]

Not being familiar with that gas block, is it a "set it and leave it alone" block? Or does it have several settings? I know there are some that have an unsuppressed setting so that when you aren't using the can it's still functional. I know my WAR upper cuts off so much gas in the suppressed setting it'll cause a stoppage running without the suppressor.

I would play with it some; dial it down and see what causes a stoppage then open the port back up gradually til it operates smoothly/reliably (you'll feel the recoil impulse lessen noticeably compared to wide open) and check for a consistent ejection pattern

[alamo5000]

Not being familiar with that gas block, is it a "set it and leave it alone" block? Or does it have several settings? I know there are some that have an unsuppressed setting so that when you aren't using the can it's still functional. I know my WAR upper cuts off so much gas in the suppressed setting it'll cause a stoppage running without the suppressor.

I would play with it some; dial it down and see what causes a stoppage then open the port back up gradually til it operates smoothly/reliably (you'll feel the recoil impulse lessen noticeably compared to wide open) and check for a consistent ejection pattern

The instructions says it has '15 useable settings' and that 'for most unsupressed shooting settings 5 to 7 are normally correct'... I guess there is nothing like a little trial and error to figure it out. To get to setting 5 you click all the way clockwise then count clicks counter clockwise. With the right tool (which I bought one) you can adjust it in 10 seconds on the fly in the field.

I am more or less wondering if there are any hard and steadfast rules, or maybe even just some rules of thumb about them that could save me some grief. I have never really messed with the gas system before so I am wondering what 'right' is supposed to look like.

[alamo5000]

For example when I did the T&E rifle the gun would shoot but it would barely flip brass out the side and would blow back far enough to snag another round but not far enough to lock the bolt. That was obviously too 'loose" for my tastes... but then I just opened it all the way up and ran it that way... I did that though for a different motive though. I wanted to see if the open port on the side of the ambi upper would have gas escaping. I didn't really test for 'optimal gas'.

I can get over gassed and I can get under gassed it could be one or the other but in a perfectly running gun is there anything special I should look for so that I can fine tune? And without putting it on a chrono do these blocks have any effect on velocity when ran with suppressors or anything like that? I don't know if bleeding off gas for the last 3 or 4 inches of the barrel would have any major noticeable effect or not. My suspicion is no but I am not sure.

[Dstrbdmedic167]

I have never really messed with the gas system before so I am wondering what 'right' is supposed to look like.

Are you referring to the proper amount of gas that is supposed to be used? If so you just need to follow the chart. I, personally, like my unsuppressed rounds to be around the 4:30 mark and my suppressed rounds to around 2:00. That's just my preference though. I usually set it to a happy medium between the two and leave it alone at that point. That's just what I do and prefer.

http://images.tapatalk-cdn.com/15/06/02/94fbdb47da2bc1d828c6bb59b4ab5bbd.jpg

[Slippers]

So many things can affect the ejection path. The above chart has lead far too many people to chase down non-existent problems.

Different strength ejection springs, extractor springs/o-rings, buffer springs, buffer weights, BCG weight, and ammo. Not to mention upper receiver design, like a Vltor MUR vs a forged ejects different due to the shape of the deflector.

I wish that chart had never circulated all over the internet.

With regards to your original question: if the rifle cycled fine without the adjustable gas block, then the gas port on your barrel is probably correct, as is your combination of buffer spring and buffer weight. You can run it wide open without any issues.

Once you have your suppressor just try it out first, and see if the recoil increases, and whether you get excessive gas in your face. You can then try turning the gas block down until you get it where you want it.

Ejection path doesn't really mean anything unless you're having malfunctions. A lot of people will argue against this, of course. It's the internet, afterall.

[alamo5000]

Are you referring to the proper amount of gas that is supposed to be used? If so you just need to follow the chart. I, personally, like my unsuppressed rounds to be around the 4:30 mark and my suppressed rounds to around 2:00. That's just my preference though. I usually set it to a happy medium between the two and leave it alone at that point. That's just what I do and prefer.

http://images.tapatalk-cdn.com/15/06/02/94fbdb47da2bc1d828c6bb59b4ab5bbd.jpg


You beat me to the punch! LOL Good job man! ;)

I found that same graphic and was was going to use it as a reference. On the T&E upper when I first got it the brass was flipping out like 3:00 until I tightened it down.

With my regular upper and with a standard block the brass ejects right about 4:30 every time.

I have a few more questions for discussion but I have to go to work now... but as in when I add the suppressor to the mix I hear the term 'back pressure'... that just seems to me to mean that the barrel gasses are trapped longer or rather 'controlled' and makes the equivalent 'psi' across the whole system go up a notch or two... which could or could not maybe lead to other issues? Having too hard of a blow back without a strong enough buffer... or any number of things...

I am not looking for Bill Nye the Science Guy to explain it all (but I am a nerd like that so if you can go for it).... but I am just talking in general how is my gas system going to be effected with the adjustable block and more specifically shooting suppressed.

Adjusting it unsuppressed is easy enough. I am not worried about that. But when I put the suppressor on I kind of want to know what's all going on.

[Slippers]

Seriously, ignore that chart. Ugh.

Edit: where's iraqgunz when you need him? :)

[Dstrbdmedic167]

Seriously, ignore that chart. Ugh.

Edit: where's iraqgunz when you need him? :)

I should have added that the chart is a reference and should be taken with a grain of salt. I've just found that when I get my rifle tuned like I want it that is where things fall.

[Slippers]

Alamo,

When you use a suppressor, it's somewhat like having a longer barrel without moving the gas port (or changing the gas port diameter). The suppressor traps the gases behind the bullet, which increases the dwell time. Dwell is the span of time where a bullet is still in the barrel but past the gas port, so gas is bleeding off to cycle the action. With more gas coming back into the bolt carrier group, it has to go somewhere, so it tends to vent out the back of the charging handle, plus the ejection port, and down into the lower receiver. You'll be able to tell where it's going by examining all the carbon buildup throughout your rifle. :)

Velocity is not going to be affected by closing off the gas port using your adjustable gas block. You might see a very small increase in velocity from having the suppressor on, but it's negligible.

Also, regardless of whether you use an adjustable gas block or not, you'll still get some crud coming back into the chamber directly from the barrel whenever you shoot suppressed. This is why people who see piston ARs as superior for suppressor use have probably never even shot the combination (or had to clean it). They run just as dirty as DI ARs when both have a suppressor.

[alamo5000]

Good discussion so far. Thanks for all the replies. I've seen that chart before but my ideas are "if it ain't broke don't fix it" LOL. My rifle shot fine with the standard stuff. Rainier makes good stuff so what the hey... That said now I am dipping my toe into the water about to jump into the pool so the more I know the better.

OK ...back to making donuts. LOL


Keep it coming guys. After I get off work I will read over everything in more detail.

[Former11B]

Keep it coming guys. After I get off work I will read over everything in more detail.

Unless you have more questions, Slippers' last post was on the money.

I was going to say something similar about a piston gun vs a DI when running suppressed, but that's been covered.

Some suppressors by design produce less back pressure like a reflex style versus a regular muzzle-forward can. Ever seen the OSS suppressors? The muzzle device looks like some high dollar steam punk accessory Id be afraid to put through a windshield...but I digress. The OSS can was designed to have minimal back pressure but it didn't suppress nearly as well as cheaper alternatives

[VIPER 237]

Seriously, ignore that chart. Ugh.

Edit: where's iraqgunz when you need him? :)

Please take his advice. As you said that chart should be burned and erased from the Internet.

[alamo5000]

Slippers has once again proven that he knows his stuff. Thanks guys for all the answers.

When I get a chance to shoot some with the adjustable gas block on there I think I will tinker around with it and see if the manufacturer's suggested settings do anything.

But like I said it ran like a charm with a standard gas block so worst case scenario I will open it up all the way and run like normal until my suppressor gets here... then I will mess with it again.

And duly noted about the chart :)

Oh, I do have a question though... one more... do you ever have to clean the port on the adjustable gas block? I mean if there is a bunch of dirty gas blasting through there it only makes sense that it needs to be cleaned every now and again. Yes? No?

[WHSmithIV]

Are you referring to the proper amount of gas that is supposed to be used? If so you just need to follow the chart. I, personally, like my unsuppressed rounds to be around the 4:30 mark and my suppressed rounds to around 2:00. That's just my preference though. I usually set it to a happy medium between the two and leave it alone at that point. That's just what I do and prefer.

http://images.tapatalk-cdn.com/15/06/02/94fbdb47da2bc1d828c6bb59b4ab5bbd.jpg

What I like about this chart is the pink side [:)]

[SwissyJim]

Slippers has once again proven that he knows his stuff. Thanks guys for all the answers.

When I get a chance to shoot some with the adjustable gas block on there I think I will tinker around with it and see if the manufacturer's suggested settings do anything.

But like I said it ran like a charm with a standard gas block so worst case scenario I will open it up all the way and run like normal until my suppressor gets here... then I will mess with it again.

And duly noted about the chart :)

Oh, I do have a question though... one more... do you ever have to clean the port on the adjustable gas block? I mean if there is a bunch of dirty gas blasting through there it only makes sense that it needs to be cleaned every now and again. Yes? No?

I have SLR adj blocks on all my guns now... I love them. I have not cleaned the port itself, but you will want to adjust the screw that changes the settings every so often. I do it when I clean the gun. Otherwise, with all the crap from the suppressor can potentially lock up the adjustment screw. On the Sentry, it's not as big of an issue since there is the inspection cover or whatever it is. You can remove that and put some CLP on the parts and they will break free (speaking from experience). I had an older model SLR block that the adj screw locked up so tight I stripped out the head trying to break it loose. I never adjusted that one once I got it set for my loads. Todd was nice enough to send me a replacement, and the upgrade to the Sentry model to boot. Andsince then, I make a point to adjust them on occasion.

[alamo5000]

I have SLR adj blocks on all my guns now... I love them. I have not cleaned the port itself, but you will want to adjust the screw that changes the settings every so often. I do it when I clean the gun. Otherwise, with all the crap from the suppressor can potentially lock up the adjustment screw. On the Sentry, it's not as big of an issue since there is the inspection cover or whatever it is. You can remove that and put some CLP on the parts and they will break free (speaking from experience). I had an older model SLR block that the adj screw locked up so tight I stripped out the head trying to break it loose. I never adjusted that one once I got it set for my loads. Todd was nice enough to send me a replacement, and the upgrade to the Sentry model to boot. Andsince then, I make a point to adjust them on occasion.

This is good information to know. So every now and again just click it around a bit... maybe close it off and open it to keep it from locking up.... About how often are we talking I do that?

Again extremely valuable information. Thank you.

[SwissyJim]

This is good information to know. So every now and again just click it around a bit... maybe close it off and open it to keep it from locking up.... About how often are we talking I do that?

Again extremely valuable information. Thank you.
I think I do it when I clean the gun... when I think of it. The one I had that locked up (older style) probably had 500-1000 rounds thru it, 90% suppressed. I probably adjust the current one (Sentry) every 200 rounds or so? And all I do is adjust fully one direction then the other -and make sure you count clicks so you can put it back to the same setting! If you forget, or it does freeze up, all you have to do is remove the small screw and plate on the side and add some CLP to the parts. Then carefully try to adjust the setting screw. You'll find that it will break up the crap and start moving again pretty easily.

And unless you are shooting suppressed, it's probably not needed. But trust me.. .once you get your can, there is no reason NOT to shoot suppressed all the time!

[alamo5000]

But trust me.. .once you get your can, there is no reason NOT to shoot suppressed all the time!

I trust you and the ATF already has my money [:D]

I can only hope that they will not take forever....but I am trying not to think about it.

[amphibian]

So many things can affect the ejection path. The above chart has lead far too many people to chase down non-existent problems.

Different strength ejection springs, extractor springs/o-rings, buffer springs, buffer weights, BCG weight, and ammo. Not to mention upper receiver design, like a Vltor MUR vs a forged ejects different due to the shape of the deflector.

I wish that chart had never circulated all over the internet.

With regards to your original question: if the rifle cycled fine without the adjustable gas block, then the gas port on your barrel is probably correct, as is your combination of buffer spring and buffer weight. You can run it wide open without any issues.

Once you have your suppressor just try it out first, and see if the recoil increases, and whether you get excessive gas in your face. You can then try turning the gas block down until you get it where you want it.

Ejection path doesn't really mean anything unless you're having malfunctions. A lot of people will argue against this, of course. It's the internet, afterall.

+1....I agree totally with you but at the same I do have mixed opinion on the chart.

You are totally spot on that so many things can affect the ejection pattern and I like to point out that I definitely do not trust it with 300 BLK since the case is shorter and impacts the upper differently than 556 does.

However, I think that if all the variables are known then why ignore the ejection pattern?

Having a 1 o'clock ejection pattern is a SYMPTOM of overgassing but again is not 100% accurate.

If someone is coughing that doesn't mean that person has the flu does it? Of course not, however if someone is PROVEN to be having the flu then coughing is to be expected.

Likewise, 100% of the time when I encounter a 556/223 AR/M16 that IS overgassed, it WILL eject at the 1 o'clock area while a properly gassed AR will eject more around the 3:30 - 4:30 area....but this is with a milspec upper, BCG etc...

Just like seen in the video below.
Crane spec's out .070 for the 10.3" MK18, M855 and H2 buffer and it runs at 830 RPM and clearly ejects around the 4 o'clock area.
While running a suppressor at the same .070" port it is overgassed and clearly ejects around the 1 o'clock area.
How do we know we know it is overgassed? You can clearly see an increase of almost 200 RPM faster in the cyclic rate and all the gas blowing out of the ejection area and in your face. You can also feel the increase in recoil when overgassed.
Running a .049" port brings the full auto ROF back down to where it should be, lack of gas being thrown out of the ejection port, ejection back in the 4 o'clock area and a much smoother recoil impulse.
So it obviously PROVEN to be overgassed since the same exact firearm and ammo is now functioning fine with a .049 gas port.

Again, I definitely see your point about ignoring the ejection pattern and I think the issue here is that too many people don't have a baseline to compare it to. If you just look at an AR firing and see the it ejects at 1 O'clock then you don't go through the steps of quantitatively making the gas port smaller then you really don't know if it is overgassed or not.

However, ignoring the ejection pattern in what is clearly overgassed in an AR/M16 that IS actually PROVEN to be so wouldn't be very observant for troubleshooting POSSIBLE issues.


http://www.youtube.com/watch?v=Se2QsKuX2xM

[alamo5000]

I did my first shooting with my new gas block today... man... that thing makes a difference. The instructions say 'most AR's will run on position 5-7'... on position 5 my bolt will not lock back. On position 6 it will. I shot the gun on several positions and my shots were all over the board. Adjusting the gas seemed to effect accuracy but I will take my sled out and confirm. On the different settings I was getting vastly different impact points and spreads. That said I JUST reinstalled my scope back on my rifle so there is a possibility of that having an effect but it appears that altering the gas alters the accuracy (at least at first glance).

The most I went up to was setting 8 (out of 15). I tailored my rounds to run on a standard block and was getting sub MOA with that so I am guessing if I open it all the way up I would replicate that. At first look that gas block is adding a whole new element to my attempts to be 'very accurate' (sub moa) and maybe to load development.

I will break out the sled tomorrow and do more testing and try to document what happens.

[GOST]

Look forward to hearing about your results with the sled.

[alamo5000]

Look forward to hearing about your results with the sled.

One thing I already found... I was suspicious at first but I just sat the rifle down until I had a fresh mind where I could check it over. Just now I found the front screw on my scope mount was loose.... really loose. I think I found the culprit right there but there is no telling.

My little bit of shooting this evening was rather hastily arranged so I think there was also a fair amount of shooter error. (Basically I left work kind of irritated but the weather was nice so I figured I would try to do something to get my mind clear)... long story short I was shooting but not paying attention to details like I normally do. I was just trying to have some fun.

I think the scope mount coming lose explains a lot... but I am still going to do my tests just because I want to and because it's America [:D]. I'm going to sleep on it and see if I can come up with a good way to test. I do know now though that scope problem or not, position 6 is the minimum to lock my bolt back. This much I know. :P

[alamo5000]

A quick report... I didn't have all day to mess with things so I will have to have an ongoing test as I see this is going to be a long process.

First off somehow or another my scope was off. So after I tightened everything down I didn't touch anything adjustment wise, but I did fix the loose mount problem.

I did several small test batches starting with setting 6. I started there because that is the minimum before my bolt will not lock back.

On setting 6 3 shots were all 3" high and 1" to the left of my aim point.**

Without changing a thing I put it on setting 7.

3 shots were 1 1/2" high 1" left.

Without changing a thing I put it on setting 8 still using the same exact aim point.

3 shots were 2 1/2" high and 1" left

----

With setting 6 and setting 8 my groups were about an inch or so in a clear cut triangle pattern. With setting 7 I stacked 2 shots that were literally a same hole impact and one shot was about 1/2" left of the other two.

Maybe it was the luck of the draw but I chose setting 7 and re-zeroed my rifle. Before I was all done I was able to get 7 shots on a 3/4 inch sticker that I was using for my aim point. I had a couple of flyers. I just counted and I had 7 on and 3 flyers, which could have been shooter error, mixed brass or any number of things.

Now that I know I am zeroed at setting 7 I am going to revisit this over time. I got it set to where it works so that's all good.

So now going forward I can use that as a baseline to test impact shifts. To me though even though my batches were kind of small samples I at least think I was seeing a difference in impact. It's still a hypothesis and a theory not a proven fact, but over time I will try different gas settings and see if there is noticeable shift.

**I hadn't noticed but I had changed the horizontal knob two clicks to the left when I was using the old upper and never put it back until after this test when I was re zeroing.