Adjustable Gas Block Questions

[alamo5000]

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



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.

[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.

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.

What I like about this chart is the pink side