Can over gas destroy accuracy?

[SonoranPrecision]

I have a more precision oriented ar15 build that has always been pretty over gassed. It’s a 16” mid length gas, and had 1:30 ejection with mk262, running a standard weight spring and h2 buffer.

I recently added a sprinco blue spring and an h3 buffer, and that brought the ejection to about 2:30 or 3, and precision seemed to improve, but only slightly. Say from 1.25 moa 10 shot groups to 1 moa.

The other day I got a TBAC ultra 7 out of jail and promptly took it to the range, only to find out it opened up the groups to 2-3 moa with some diagonal stringing, and ejection was up around 12:30-1:00. Took the can off and everything went back to normal.

I know it’s not the suppressor, as I put it onto another known good rifle and it shot as expected for that rifle.

So my question is, can an ar15 degrade accuracy that much simply from over gas? Or is it more likely that this particular barrel just really hates being suppressed?

 

[OREGUN]

AGB on that blaster?

 

[SonoranPrecision]

AGB on that blaster?

Unfortunately not, I put it together years ago and wasn’t even considering suppressing it at the time.

 

[TonyTheTiger]

Friends don't let friends buy 16" mid gas.

 

[Rocketvapor]

To confirm it's gas or not, move gas block to cut off gas.
Try it with and without the can.

 

[SonoranPrecision]

To confirm it's gas or not, move gas block to cut off gas.
Try it with and without the can.

That’s a good idea, hadn’t thought about that

 

[OREGUN]

Close off the gas system and try some without. But if you are going to that length, moving the gas block, I’d just get an adjustable and try that.

 

[OREGUN]

I’d still be curious if a gas gun expert has an answer to the original question. The can changes a lot of things all at once so is it the over gas that’s causing the problem or something else? Got another can you can try?

 

[SonoranPrecision]

Got another can you can try?

Sadly no, unless someone else in az has a bunch of TBAC CB compatible cans they’d let me try out lol

 

[msgriff]

What other rifle did you try the Ultra 7 on?

 

[wade2big]

Friends don't let friends buy 16" mid gas.

Who makes a good lightweight 16” rifle gas 556 barrel for a general use carbine? Right now my carbines have BCM 16” mid length ELW profile barrels in them. What would be comparable but with the longer gas system?

 

[SonoranPrecision]

What other rifle did you try the Ultra 7 on?

A couple bolts guns, but the one I was talking about is an 11lb 300wsm that put 14 rounds into about .7” at 100yds.

 

[OREGUN]

A couple bolts guns, but the one I was talking about is an 11lb 300wsm that put 14 rounds into about .7” at 100yds.

I have a virtual fleet of CB cans but I’m nowhere near PHX. The huge majority of my suppressor use is on bolt guns but I’ve only ever seen my cans improve or have no effect on accuracy expressed in 100 yard group size. They do have varying effects on chronograph stats though...so consistency, if you will. The gas pressure on an AR platform is a real thing though so it’s worth exploring the gas off results.

 

[SonoranPrecision]

I have a virtual fleet of CB cans but I’m nowhere near PHX. The huge majority of my suppressor use is on bolt guns but I’ve only ever seen my cans improve or have no effect on accuracy expressed in 100 yard group size. They do have varying effects on chronograph stats though...so consistency, if you will. The gas pressure on an AR platform is a real thing though so it’s worth exploring the gas off results.

Yeah I’ll definitely mess with it a little bit.

 

[tucaz]

Who makes a good lightweight 16” rifle gas 556 barrel for a general use carbine? Right now my carbines have BCM 16” mid length ELW profile barrels in them. What would be comparable but with the longer gas system?

FN. midway sells them.

 

[BillyBob13]

My first thought would be to double check the concentricity of your barrel threads / shoulder. Also, do the barrel threads have a proper relief cut? Accuracy issues with a suppressor very often stem from an issue with the barrel threads / shoulder. Or, an installation issue with the suppressor mount (CB mount) - bent peel washer, etc. that is throwing things out of alignment.

 

[TonyTheTiger]

Who makes a good lightweight 16” rifle gas 556 barrel for a general use carbine? Right now my carbines have BCM 16” mid length ELW profile barrels in them. What would be comparable but with the longer gas system?

Depends on your standards I guess. SOT, KAK, Spinta and some others make lightish profile nitrided barrels that are very acceptable for regular carbine use. Criterion makes a Hybrid contour barrel that is great, but unfortunately front heavy. Iron City Rifleworks used to make one, the one I own is a laser. Rainier (yeah I know) has a couple options, the Select series being more of the hard use type, as well as some precision type barrels. Then you can always get a custom, but they will typically be SS precision type barrels that aren't CL or Nitrided.
Intermediate gas 16" barrels are great too, probably more so than RLGS if you aren't into tuning AR's.

 

[TonyTheTiger]

FN. midway sells them.

Link? Couldn't find them.

 

[DHDeal]

Depends on your standards I guess. SOT, KAK, Spinta and some others make lightish profile nitrided barrels that are very acceptable for regular carbine use. Criterion makes a Hybrid contour barrel that is great, but unfortunately front heavy. Iron City Rifleworks used to make one, the one I own is a laser. Rainier (yeah I know) has a couple options, the Select series being more of the hard use type, as well as some precision type barrels. Then you can always get a custom, but they will typically be SS precision type barrels that aren't CL or Nitrided.
Intermediate gas 16" barrels are great too, probably more so than RLGS if you aren't into tuning AR's.

Kinda waiting on the Criterion Hybrid RLGS 16" to come back in stock (if ever). My current 16" is an Intermediate Odin Works. Not a bad barrel at all but not a lightweight either.

 

[tucaz]

Link? Couldn't find them.

looks like the CHF are OOS right now though

FN Barrel AR-15 5.56x45mm 16 Government Contour Carbine Length Gas

FN AR15 barrels are hammer forged using the same proprietary high grade Chrome Moly Vanadium steel used in FN’s venerable machinegun...

www.midwayusa.com

but the button rifled is there.

FN Barrel AR-15 5.56x45mm 16 M4 Contour Carbine Length Gas Port 1 7

FN AR15 premium button rifled barrels are are manufactured using U.S. sourced Chrome Moly Vanadium material per Mil-B-11595E. Each barrel is High...

www.midwayusa.com

they do list a 10.5” available though. just type “fn barrel” in the search bar.

 

[DHDeal]

looks like the CHF are OOS right now though

FN Barrel AR-15 5.56x45mm 16 Government Contour Carbine Length Gas

FN AR15 barrels are hammer forged using the same proprietary high grade Chrome Moly Vanadium steel used in FN’s venerable machinegun...

www.midwayusa.com

but the button rifled is there.

FN Barrel AR-15 5.56x45mm 16 M4 Contour Carbine Length Gas Port 1 7

FN AR15 premium button rifled barrels are are manufactured using U.S. sourced Chrome Moly Vanadium material per Mil-B-11595E. Each barrel is High...

www.midwayusa.com

they do list a 10.5” available though. just type “fn barrel” in the search bar.

Carbine gas system on those, not RLGS. I believe that was what being asked about. When TTT stated "Friends don't let friends buy 16" mid gas.", I am almost positve he wouldn't let enemies buy a 16" carbine gas.

Maybe I was wrong.

 

[Milf Dots]

To the Op's question: Only if you inhale.

 

[aviumvenator]

Carbine gas system on those, not RLGS. I believe that was what being asked about. When TTT stated "Friends don't let friends buy 16" mid gas.", I am almost positve he wouldn't let enemies buy a 16" carbine gas.

Maybe I was wrong.

It defaults to the carbine length. Select rifle length from the drop down.

 

[TonyTheTiger]

looks like the CHF are OOS right now though

FN Barrel AR-15 5.56x45mm 16 Government Contour Carbine Length Gas

FN AR15 barrels are hammer forged using the same proprietary high grade Chrome Moly Vanadium steel used in FN’s venerable machinegun...

www.midwayusa.com

but the button rifled is there.

FN Barrel AR-15 5.56x45mm 16 M4 Contour Carbine Length Gas Port 1 7

FN AR15 premium button rifled barrels are are manufactured using U.S. sourced Chrome Moly Vanadium material per Mil-B-11595E. Each barrel is High...

www.midwayusa.com

they do list a 10.5” available though. just type “fn barrel” in the search bar.

I think we've got a couple different trains of thought going in this thread. For my part, I was just expressing my distaste for anything shorter than intermediate on a 16" barrel.

Carbine gas system on those, not RLGS. I believe that was what being asked about. When TTT stated "Friends don't let friends buy 16" mid gas.", I am almost positve he wouldn't let enemies buy a 16" carbine gas.

Maybe I was wrong.

Yeah that's what I was getting at.

 

[LRRPF52]

I have a more precision oriented ar15 build that has always been pretty over gassed. It’s a 16” mid length gas, and had 1:30 ejection with mk262, running a standard weight spring and h2 buffer.

I recently added a sprinco blue spring and an h3 buffer, and that brought the ejection to about 2:30 or 3, and precision seemed to improve, but only slightly. Say from 1.25 moa 10 shot groups to 1 moa.

The other day I got a TBAC ultra 7 out of jail and promptly took it to the range, only to find out it opened up the groups to 2-3 moa with some diagonal stringing, and ejection was up around 12:30-1:00. Took the can off and everything went back to normal.

I know it’s not the suppressor, as I put it onto another known good rifle and it shot as expected for that rifle.

So my question is, can an ar15 degrade accuracy that much simply from over gas? Or is it more likely that this particular barrel just really hates being suppressed?

You need to choke the gas flowing back into your bolt carrier expansion chamber.

I personally use Bootleg Adjustable Gas carriers, which are easy to adjust through the ejection port with a flat head.

Others have been having great results with Riflespeed adjustable blocks with 12 positions.

I built 2x 6.5 Grendels with 12” CLGS barrels, one of which got a 5” Ultra and the other an Ultra 7. Both have Bootleg carriers set at fully-choked when suppressed, both run great. I’ve shot my 12” for 7 years, 6 of those suppressed with the Ultra 5.

Ejection can easily be set at 4-4:30.

 

[Naaman]

It defaults to the carbine length. Select rifle length from the drop down.

RLGS not available on the 16. I guess he could by the 18 or 20 and cut it. If so, I imagine resizing the gas port would be necessary as well?

 

[n2ishun]

Overgassing can kill accuracy, fo sho.
I used to have a 24" heavy with rifle length gas (will leave maker out because I'm gonna try being nice for once) that was so over gassed it would slam the bolt back so hard it made the rifle kick like a .338 mag.
Seriously, the first mag that went thru the thing when I tested it wore me out.
Obviously I got a adjustable gas block for it as soon as was possible, but that one and only mag thru it cracked the back of the buffer tube.....at that time I had no idea that could even happen.
.936 adjustables are not exactly a deeply stocked item either.
Once I got it sorted it shot fine, but those first rounds were all over a 12" bullseye, and I mean all over.
Once sorted it shot just at 1 inch, but knowing the gas port was so massively oversized I couldn't sell it quick enough.
No telling what else was out of spec.

 

[A.sosa]

Anything is possible, but I’d doubt it.

 

[tucaz]

I think we've got a couple different trains of thought going in this thread. For my part, I was just expressing my distaste for anything shorter than intermediate on a 16" barrel.

Yeah that's what I was getting at.

ah my bad for not knowing the sarc! i havent spent enough time here reading to know ins and outs

i was basing that on my own experience that carbine gas and mid never seemed to make that much difference to me. it was all about the port sizing that made the difference. i have a really well behaved fn 16” carbine gas now.

i think my favorite ar15 rifle is an 18” rifle length gas and a5 buffer though.

 

[supercorndogs]

When I was trying to get my grendel to shoot. I started with h2 and extra power spring. I finally got it shooting after switching to a carbine spring and turning the gas way down.

 

[Ledzep]

Didn't read through the thread but I tested my PRS gas gun with AGB through the functional range of gas adjustment and yes overgassing increases the occurrence and severity of errant shots.

Also, however, muzzle devices-- as simple as a 6.5mm and .30 cal version of the same brake can cause distinct dispersion differences. Brake to suppressor even bigger changes IME... So the OP is getting hit from both directions.

 

[antecedent]

When I was trying to get my grendel to shoot. I started with h2 and extra power spring. I finally got it shooting after switching to a carbine spring and turning the gas way down.

Same experience with a Grendel, was playing with gas settings, springs, and buffers, and one combination ended up way over gassed; slams the bolt/buffer back, extractor swipes + dents on case necks, plus various malfunctions and very poor accuracy. Turned the gas way down and all back to normal.

 

[Bluedog82]

Heavier springs don’t really delay unlocking, but rather assist on the return to battery.

 

[BCP]

I have a more precision oriented ar15 build that has always been pretty over gassed. It’s a 16” mid length gas, and had 1:30 ejection with mk262, running a standard weight spring and h2 buffer.

I recently added a sprinco blue spring and an h3 buffer, and that brought the ejection to about 2:30 or 3, and precision seemed to improve, but only slightly. Say from 1.25 moa 10 shot groups to 1 moa.

The other day I got a TBAC ultra 7 out of jail and promptly took it to the range, only to find out it opened up the groups to 2-3 moa with some diagonal stringing, and ejection was up around 12:30-1:00. Took the can off and everything went back to normal.

I know it’s not the suppressor, as I put it onto another known good rifle and it shot as expected for that rifle.

So my question is, can an ar15 degrade accuracy that much simply from over gas? Or is it more likely that this particular barrel just really hates being suppressed?

Take a look at the riflespeed gas block you probably want the longest one. Or try with lighter weight/lower velocity ammo.

I've got a couple green mountain barrels that are 16" mid gas and they eject normally, don't beat up brass, and my buffer and spring aren't h2 or extra power or whatever.

 

[tucaz]

I have a more precision oriented ar15 build that has always been pretty over gassed. It’s a 16” mid length gas, and had 1:30 ejection with mk262, running a standard weight spring and h2 buffer.

I recently added a sprinco blue spring and an h3 buffer, and that brought the ejection to about 2:30 or 3, and precision seemed to improve, but only slightly. Say from 1.25 moa 10 shot groups to 1 moa.

The other day I got a TBAC ultra 7 out of jail and promptly took it to the range, only to find out it opened up the groups to 2-3 moa with some diagonal stringing, and ejection was up around 12:30-1:00. Took the can off and everything went back to normal.

I know it’s not the suppressor, as I put it onto another known good rifle and it shot as expected for that rifle.

So my question is, can an ar15 degrade accuracy that much simply from over gas? Or is it more likely that this particular barrel just really hates being suppressed?

sounds like a good candidate for a BRT gas tube. i put those on a couple suppressed uppers with excellant results.

just a thought but does baffle design affect accuracy? back pressure, pressure waves inside the can? just spit balling, i'm no technician.

 

[sloporsche]

Over gassing can beat the hell out of some weapons so yes it could effect accuracy

 

[SonoranPrecision]

sounds like a good candidate for a BRT gas tube. i put those on a couple suppressed uppers with excellant results.

just a thought but does baffle design affect accuracy? back pressure, pressure waves inside the can? just spit balling, i'm no technician.

I’d never even heard of those gas tubes, that seems like a good option

 

[tucaz]

I’d never even heard of those gas tubes, that seems like a good option

i hadn't either until i started hanging out around this place! a hidden gem is information and high quality posters.

you will need to messaure your port size though. i had a bunch of machinist bits but also a caliper.

i picked my own gas port sizes and nailed it. had one 11.5 upper that was out running the mag bad and brought it down to 2 oclock. another 12.5 midlength that was a 16" barrel at one time, and my 16" carbine gas is now a 3 oclock ejector. all at deticated suppressed with old AAC cans.

AGB's didnt even help all that much for the 11.5 and it wasnt really all that big of a port at .069 and i think i went .064

 

[SonoranPrecision]

Update time.

Less (proper) gas and the rifle went back to shooting normally, around 1moa even on a hot barrel.

So I went with a BRT gas tube, and elected to let them select the proper port size based on my setup. I told them I was running 100% suppressed, with an H2 buffer and standard carbine spring, and only brass cased 5.56 spec ammo. They sent me a tube with a .065 port, and it’s perfect.

Suppressed w/ MK262 and going back to a standard spring and h2 buffer, I got ejection right at 2:45-3:00, swapped to an h3 buffer and have perfect 3:30 ejection. It now shoots softer suppressed than it ever did unsuppressed.

 

[msgriff]

There used to be a "cheat" for sizing gas port diameters using the BRT EZTune ordering page, where you let them choose the size based on your build parameter inputs. It wouldn't give you the gas tube opening diameter, but did list the part number that you could then cross-reference to their "choose your own" tubes, and get the gas port diameter equivalent. It was a bit shady, considering that their sizing method would be IP, and they finally caught on and no longer generate a part number on the ordering page when you have them size the gas tube. I never relied on that "cheat", but I have done the old DIY BRT CustomTune hack, if you know what that is. The CustomTune type method was around long before BRT sold them, and BRT no longer sells those kits.

 

[Ernest 5.56]

Assuming you spec the right tube is there any downside to running a BRT gas tube?

Seems like it gets you close enough and the rest can be taken care of through buffer adjustments

 

[SonoranPrecision]

Assuming you spec the right tube is there any downside to running a BRT gas tube?

Seems like it gets you close enough and the rest can be taken care of through buffer adjustments

I intentionally had them send me one to run suppressed with a heavy buffer, that way I can hopefully throw in a carbine buffer and still run unsuppressed. The only downside I have at the moment is the gun will not cycle unsuppressed with the H3 buffer. But I honestly have no desire to shoot unsuppressed at the moment, so I really don’t care lol

 

[Ernest 5.56]

I intentionally had them send me one to run suppressed with a heavy buffer, that way I can hopefully throw in a carbine buffer and still run unsuppressed. The only downside I have at the moment is the gun will not cycle unsuppressed with the H3 buffer. But I honestly have no desire to shoot unsuppressed at the moment, so I really don’t care lol

I would be curious how your gun would shoot suppressed with a tubb spring and carbine buffer

 

[Cascade Hemi]

Update time.

Less (proper) gas and the rifle went back to shooting normally, around 1moa even on a hot barrel.

So I went with a BRT gas tube, and elected to let them select the proper port size based on my setup. I told them I was running 100% suppressed, with an H2 buffer and standard carbine spring, and only brass cased 5.56 spec ammo. They sent me a tube with a .065 port, and it’s perfect.

Suppressed w/ MK262 and going back to a standard spring and h2 buffer, I got ejection right at 2:45-3:00, swapped to an h3 buffer and have perfect 3:30 ejection. It now shoots softer suppressed than it ever did unsuppressed.

It would feel even better with an .060" port and carbine weight buffer.

 

[SonoranPrecision]

I would be curious how your gun would shoot suppressed with a tubb spring and carbine buffer

Yeah I might play around with some different springs to see what happens.

 

[SonoranPrecision]

It would feel even better with an .060" port and carbine weight buffer.

No doubt. My next barrel will have a lot more thought put into it, especially now that cans are in the picture

 

[msgriff]

It would feel even better with an .060" port and carbine weight buffer.

Unless you're trying to discount the EZTune as an acceptable solution to to OP's issue, a BRT tube with a 0.065" opening is roughly equivalent to a 0.062" gas port. Not much of a difference from a 0.060" port.

 

[Cascade Hemi]

Unless you're trying to discount the EZTune as an acceptable solution to to OP's issue, a BRT tube with a 0.065" opening is roughly equivalent to a 0.062" gas port. Not much of a difference from a 0.060" port.

You misread my post. Reduce the gas tube port diameter .005" (.065" down to .060") and drop buffer weight. The extra weight is unnecessary with less gas. The same would also be true if the OP was reaming his own barrel ports. 16" mid length should run with M855 and .058" barrel port. Use good gas rings and reduce buffer weight to 3.0oz. I have an 11.5" mid length running suppressed on a .063 port and 3.8oz H buffer.

 

[DCC83501]

if changing out gas block or tube is not what a guy wants to do, installing an adjustable gas key is very easy and takes care of over gassing issues.

 

[SonoranPrecision]

if changing out gas block or tube is not what a guy wants to do, installing an adjustable gas key is very easy and takes care of over gassing issues.

That’s true, and I considered that option, but it could be argued that swapping a gas key and staking it properly is more involved than a gas tube, and you would still have excessive gas coming back into the receiver, increasing fouling.