Suppressors AR action not cycling fully with TBAC 30P-1 attached

[rg1911]

A search of the forum didn't return any threads dealing with this particular problem. I may have used sub-optimal search terms.

I have an AR-15 and an AR-10 (260 Rem) that function correctly without the suppressor attached.

Both fail to cycle completely when the suppressor is attached. That is, the bolts do not lock back on an empty magazine. I was single-loading, so I can't say if the bolt cycled enough to pick up the next round, but I suspect it does not.

Zak at TBAC suggested trying a new magazine in the AR-15 on the theory that the bolt was cycling too fast and a weak mag spring might not raise the follower quickly enough. I have not made that test, yet.

The magazine for the AR-10 is a new Armalite 10-round mag, so I am assuming the spring is in good shape.

There is no indication of a baffle strike. For instance, the AR-10 put 5 rounds into 1 inch at 200 yards.

Has anyone heard of, or experienced, this problem and found a fix?

Thank you,
Richard

 

[Zak Smith]

Typically an AR style rifle that is in the middle of its operating region will not be adversely affected by mounting a suppressor.

If it's already biased to failure or its operating window is very narrow, the additional backpressure may cause issues.

In the absence of a suppressor, failure to lock back is typically a symptom of either (1) the bolt carrier group not actually making it back far enough to lock or (2) the the follower not being raised in time.

If this is happening with additional gas pressure from the suppressor then the most likely case is that the bolt carrier group is cycling too fast for the follower to rise in time.

In this case, an adjustable gas block will likely remedy the problem.

 

[rickyd_55]

You might look into trying some different buffers and buffer springs or even an adjustable gas block.

 

[rg1911]

Thanks for all the suggestions.

Am I correctly understanding that the purpose of an adjustable gas block would be to slightly *reduce* the amount of gas being vented back to the bolt?

Thank you,
Richard

 

[Chucky]

Try a heavier buffer and you should be good. It sounds like your bolt is moving to fast for the bolt catch to come up in time before the bolt is already past it. The majority of the time you can switch to a heavier buffer and it will not cause any kind of reliability issues. An adjustable gas block is nice but most of the time it is not necessary. I don't even know how many suppressor hosts I have any more off the top of my head but I know only two of them have adjustable gas blocks and they came like that from the factory. The rest of them I just run a heavier buffer and call it good.

 

[rg1911]

Try a heavier buffer and you should be good.

Chuck,

This is something I was planning to do because the indications were that, even without the suppressor, the bolt was starting to cycle before the case neck released from the chamber. I was going to wait a while to get the heavier buffer because turning the necks of all my Lapua brass eliminated the ejection problems, but I think I'll go ahead and order one asap. If the bolt is cycling more quickly, it could be counteracting the effects of turning the necks.

Thank you,
Richard

 

[Chucky]

Richard,

If you are running an over gassed gun without the suppressor definitely get a heavier buffer or an adjustable gas block now rather than later. The faster that bolt is cycling the more wear and tear you are putting on your rifle. When you put the suppressor on you are adding even more back pressure to your rifle and you are making the problem even worse. You can either get a heavier buffer and slow down the bolt speed or get an adjustable gas block to restrict the amount of gas coming back through the gas tube. Either way you should fix it sooner rather than later.

 

[rg1911]

Richard,

If you are running an over gassed gun without the suppressor definitely get a heavier buffer or an adjustable gas block now rather than later.

Chuck,

I just ordered a buffer from Clint/Heavy Buffers. If that doesn't completely solve the problem, I'll try to find an adjustable gas block that adjusts from the front and that will fit the very fat barrel on the AR-10.

Being new to suppressors and to larger-caliber ARs, I missed the connection between over-gassing, extra back pressure, and cycling problems.

Thanks to your clear explanation, I now have a much improved understanding of what is happening.

Cheers,
Richard

 

[ORD]

Follow Zac's advice above. An adjustable gas block will allow you to get right to the suspected (and overwhelmingly likely) cause of the failure which is significant overgassing causing the bolt to override the bolt catch/stop.

With an adjustable block, you'll be able to both optimize functioning non-suppressed (on what are probably overgassed rifles at least to some degree now) and suppressed (in which case they are WAY overgassed due to the increased blowback/pressure).

A heavy buffer, while it will at least help with the situation (and maybe even resolve it), is but a proverbial bandaid for a sucking chest wound. Get to the root cause of the problem and fix it there with an adjustable gas block on each rifle and skip the additional reciprocating mass.

 

[Chucky]

Richard,

Not a problem. Glad I could be of help. Depending on how over gassed the rifle is the buffer will at least slow down that bolt speed and hopefully also fix the bolt catch issue. Good luck.

 

[rg1911]

Follow Zac's advice above. An adjustable gas block will allow you to get right to the suspected (and overwhelmingly likely) cause of the failure which is significant overgassing causing the bolt to override the bolt catch/stop.

Undoubtedly good advice. But I was able to find the buffer and I haven't yet found a block that's adjustable from the front and that will fit my barrel. I'm sure there's one out there; just need to search more.

So, I'll try the band-aid until I can find the correct block.

Cheers,
Richard

 

[Zak Smith]

What's the OD of the barrel at the gas block?

 

[ORD]

+1 on knowing the barrel/journal size, along with the handguard you are needing to fit it under.

In any event, the best front adjustable designs are those from SLR Rifleworks as well as Syrac Ordnance. SLR's newest "Sentry" design is small enough to fit just about any combo on the market, but not all the sizes are available yet (should be in the next couple months MAX before all will be ready to roll).

 

[Gunfighter14e2]

Has anyone heard of, or experienced, this problem and found a fix?

Factory ammo or home grown?
If factory ammo it's a minor mechanical fix, if home grown it's simpler yet. Your powder burn rate is too fast, or your over pressure.

 

[rg1911]

What's the OD of the barrel at the gas block?

*That's* what I forgot to do last night. I'll check after work today.

Richard

 

[MicroMOA]

A heavy buffer, while it will at least help with the situation (and maybe even resolve it), is but a proverbial bandaid for a sucking chest wound. Get to the root cause of the problem and fix it there with an adjustable gas block on each rifle and skip the additional reciprocating mass.

+1, an H2 buffer is all that is needed to stop bolt bounce (at least for 5.56) and that is all I use. As mentioned any heavier and you are just adding reciprocating mass.
Heavy buffers also don't do anything to reduce the fouling.

My patented tool less adjustable gas block adjusts from the side vs the front. Depending on the rail you may able to do this with your finger. In most cases you need something to push it and in most cases a bullet will do like pictured below:

In addition, with this design you know what position your regulator is in by look or by feel in complete darkness.

It is also based on actual port sizes vs just obstructing the path of the gas with a set screw where you have no quantitative idea on how big your port is.

I would figure out how bit the port is in your barrel then drill one port to match that which will be your adverse conditions port since that is the max it can go. Use that as your alignment/install position as shown below:

Once you've done that you drill out the other position or other 2 positions to whatever you want or don't drill if you want to kill the gas completely.
I'm talking about our custom offerings, we offer regulator plates pre-drilled for those that don't want this level of fine tuning.

We have a state LE agency using a 3 position configuration of optimal-unsuppressed/suppressed/adverse. Again the adverse simply matches the port in the barrel. They use Simunitions which is weaker than their duty loads. Before they were swapping buffers/springs out when going to the Simunitions and now they just move the regulator over to the adverse to run the Simunitions. It is also dual function for use when using duty loads and if the gun is too dirty to function. Then of course suppressed is for suppressed.

Plenty more info, pics and videos here: MicroMOA - Home of the Govnah - Modular Adjustable Gas Block

 

[rg1911]

What's the OD of the barrel at the gas block?

It's .937 in front (muzzle end) of the gas block.

Have now been pointed to a couple gas blocks that look like they'll work, assuming one or more will fit under the hand guard.

Thank you for your help. I'll get things running correctly.

Cheers,
Richard

 

[ORD]

It's .937 in front (muzzle end) of the gas block.

I found several gas blocks listed as having a .936 bore, but haven't found one that adjusts from the front. I don't want the adjustment screw hidden under the hand guard.

See here: Sentry 9 Series

As I said above in one of my earlier posts...since you'll be running the block under your handguard, you'll need to measure (TWICE) to ensure that the SLR block will have sufficient clearance without touching the ID of your rail, but I can personally attest to the high quality/reliability/ease of adjustment (from the front) of the SLR blocks. They are one of the best designs if not the best design on the market right now for their type of block!

Good luck!

 

[rg1911]

See here: Sentry 9 Series

you'll need to measure (TWICE) to ensure that the SLR block will have sufficient clearance without touching the ID of your rail, but I can personally attest to the high quality/reliability/ease of adjustment (from the front) of the SLR blocks.
Good luck!

Thank you for that reminder.

How does the SLR compare to another .936 I finally stumbled across, the Syrac?

I see that there are clamp-on and set screw blocks. Is there an advantage of one system over another?

Richard

 

[ORD]

The new, Gen 2 Syrac and the SLR Sentry blocks share a lot more in common that their earlier, respective generations did. They are both high quality blocks, offer similar adjustment systems (click-detent, 15-16 position) and are both single-tool, front adjustable. The devil is always in the details though and the SLR is, at least in my opinion, made of slightly better components (at least internally) and their new 0.936" Sentry blocks do NOT require use of a straight gas tube which the Syrac 0.936" DOES require one. Its another 1-off component that you have to add to the system and its already higher price point, and, depending on your handguard setup, etc., the straight tubes can cause additional fitment issues.

As for clamp-on and set-screw...I prefer the clamp-on designs for a precision rifle, but both will do the trick. You generally should have your barrel properly dimpled for use with a set-screw type block, but it ain't rocket science to do it if that's the direction you want to go. Usually bottom clearance isn't an issue with these blocks (usually the taller, top portion that causes fitment issues) but the set-screw styles are usually lower profile than the clamp-on style.

 

[branson1369]

The Slash heavy buffer and JP SCS buffers fix most I have seen

 

[rg1911]

The new, Gen 2 Syrac and the SLR Sentry blocks share a lot more in common that their earlier, respective generations did. They are both high quality blocks, offer similar adjustment systems (click-detent, 15-16 position) and are both single-tool, front adjustable. The devil is always in the details though and the SLR is, at least in my opinion, made of slightly better components (at least internally) and their new 0.936" Sentry blocks do NOT require use of a straight gas tube which the Syrac 0.936" DOES require one.

Ord,

Many thanks. I now have enough information with which to work. Sounds like the SLR clamp-on is in my immediate future for at least two of my ARs. (Hope they fit under the guards. I'll measure the clearance right now.)

Cheers,
Richard

 

[rg1911]

Update:

The heavy buffer worked. That is, the bolt locked back on an empty mag and also fed the next round from a full mag. None-the-less, I just received the Sentry 9 adjustable block from SLR Rifleworks. Assuming it works correctly, I'll be getting three more for my other ARs.

Cheers,
Richard

 

[ORD]

Update:

The heavy buffer worked. That is, the bolt locked back on an empty mag and also fed the next round from a full mag. None-the-less, I just received the Sentry 9 adjustable block from SLR Rifleworks. Assuming it works correctly, I'll be getting three more for my other ARs.

Cheers,
Richard

Glad to hear the heavy buffer got you sorted out, Richard. Best of luck with the Sentry AGB. I think you'll be VERY pleased with the results/flexibility it affords you. Also, hang on to your standard wt buffer/spring just in case. Once you get the Sentry installed, you can remove the heavy buffer and tune the AGB for reliable function with the lighter buffer (for both suppressed and non-suppressed fire) if you prefer. Remember, less reciprocating mass in any AR-platform rifle is a GOOD thing!

 

[rg1911]

Remember, less reciprocating mass in any AR-platform rifle is a GOOD thing!

Ord,

That's one of the reasons I decided to go with an adjustable block.

Again, thank you (and all others) for your help.

Cheers,
Richard