AR suppressor problem

[DiggeR12]

Im trying to figure out why an AR in 7.62x39 operates fine when unsuppressed but jams every shot or every second shot when firing suppressed?

Shooting from a 16” barrel and a SilencerCo Omega300

is the rifle with suppressor on not getting enough gas to operate correctly or maybe getting to much gas and failing to operate correctly? Any ideas?

Thanks ahead of time.

 

[oldrifleman]

Probably Too much and is severely over gassed

 

[redbullitt]

^ I'd bet that! You're running the bolt too fast for it most likely.

Could try lower power ammo. Easiest would be to throw a heavier buffer in there and see if it changes.

Adjustable gas block or Adjustable carrier can help/fix too!

 

[Broncovan]

Way over gassed. Too much gas can do weird things.
Saw it in a 6.5cm build.

 

[Clayman]

Likely way too much gas.

 

[waveslayer]

Can I take too much gas for 500? Jk.

Too much gas. Slow down the bolt

 

[Flexible Tangerine Sprite]

I really do not think anyone can make a decent analysis of your AR issue from only the basic info provided. First off, running a 7.62 x 39 in an AR-15 is (and has always been) temperamental since the 7.62x39 cartridge was made for a magazine that is curved (like an AK magazine), but since and AR-15 has a straight mag well, there's always a magazine and feeding issue because the magazine needs to be straight for the first few inches. Even if a feeding issue does not always present, the situation is temperamental at best with a 7.62x39 in an AR-15. Second, to properly analyze things one needs to see exactly how the jams are occurring and how the cartridges become stuck. Not all jams are the same. I keep seeing posts about over gassing in AR's but, in truth, by their very gas system design, over gassing is almost a non-existent issue in AR's. I can go into this in more detail but out of literally hundreds of AR's I have built up, worked on and test fired (many of them wildcats), I have essentially never seen over gassing to be an issue. Odds are there is something else going on than over gassing.

 

[mettee]

If it operates fine without the suppressor, and it doesn't when you add the suppressor, then the suppressor is causing the issue. I asusme no change to ammo.

Since we all know the suppressor is going to increase gas port/gas tube pressure during dwell, the gas flow or volume is increased. Thus the terminology "over gas."

If you can't control every aspect of the build and a gas port is larger than needed how do you remedy that? Do you trash the barrel and start over?

...adding a suppressor completely changes everything when it is not flow through(typically). It changes rearward bolt speed by a lot which causes many of these issues. Most people do not shoot suppressed and never have so they do not understand the dynamic being created.

Over gas conditions being non existent doesn't compute, so if you can explain Tangerine, I'd love to learn some of what you know. Consideration for rifles being suppressed of

 

[mettee]

Double tap

 

[TonyAngel]

Im trying to figure out why an AR in 7.62x39 operates fine when unsuppressed but jams every shot or every second shot when firing suppressed?

Shooting from a 16” barrel and a SilencerCo Omega300

is the rifle with suppressor on not getting enough gas to operate correctly or maybe getting to much gas and failing to operate correctly? Any ideas?

Thanks ahead of time.

I see problems with x39 rigs pretty often. 7.62x39 barrels that I've seen tend to be over gassed as it is, and then you're compounding things by adding the suppressor.

It's kind of hard to accommodate the broad range of quality in 7.62x39 ammo, so manufacturers tend to err on the side of caution and go big on the gas port.

Which buffer and spring are you running now?

I don't want to knee jerk into telling you to go run out and get an H3 buffer and springco spring without more info.

What is your level of proficiency when it comes to working on ARs?

On my 7.62x39 rig, I run duramag mags, an H2 buffer and a Springco blue spring and used an adjustable gas block to tune to the setup. I run that setup because the H2 buffer and heavier spring help with feeding. Some ammo is just down right rough and peeling them off of the magazine is a chore for the action.

Just be aware that tuning it to run suppressed and unsuppressed on supers could be kind of a chore with a high pressure can. If this is your goal, maybe go with an H buffer unsuppressed and tune the gas block to that. This way you can go to an H3 when running the suppressor.

Honestly, you'll get the most tuning overhead by going to an A5 buffer system. I guess it depends on how invested you are in running 7.62x39.

I all but abandoned it for 300BO.

 

[mettee]

I think a lot of suppressed ARs benifit from an A5 length buffer system. If you do not change to an A5 system, the next thing I'd do is add a lot of buffer weight(probably a slash). I know this goes against what some say but the heavier buffer causes the mentioned "problems" typically when paired with stiffer springs. The extra spring tension is what typically causes the issues.

Realistically, an adjustable gas block, heavier buffer, and spring change would be the most flexible combination of parts that would help solve all the issues. But you could first try the heavy buffer. Then spring change. Then add the gas block.

 

[Gtscotty]

I really do not think anyone can make a decent analysis of your AR issue from only the basic info provided. First off, running a 7.62 x 39 in an AR-15 is (and has always been) temperamental since the 7.62x39 cartridge was made for a magazine that is curved (like an AK magazine), but since and AR-15 has a straight mag well, there's always a magazine and feeding issue because the magazine needs to be straight for the first few inches. Even if a feeding issue does not always present, the situation is temperamental at best with a 7.62x39 in an AR-15. Second, to properly analyze things one needs to see exactly how the jams are occurring and how the cartridges become stuck. Not all jams are the same. I keep seeing posts about over gassing in AR's but, in truth, by their very gas system design, over gassing is almost a non-existent issue in AR's. I can go into this in more detail but out of literally hundreds of AR's I have built up, worked on and test fired (many of them wildcats), I have essentially never seen over gassing to be an issue. Odds are there is something else going on than over gassing.

You keep seeing posts about it because it's absolutely an issue that lots of folks have and are able to easily sort out. Your assertion in this and the other thread that over gassing cannot exist in an AR, isn't an issue and can't cause feeding issues is just plainly incorrect from a mechanical systems viewpoint.

Change in the total impulse from the gas system acting on the BCG will absolutely change the momentum and, for a given total weight and spring constant, will change the rearward speed of the BCG. The fact that the gas starts venting after the bulk of the impulse doesn't mean that impulse can't be larger or smaller, or that there is no force on the BCG even when venting.

As the BCG is traveling rearward, the magazine has to be pushing the next round up and into place because the Bolt will be in position to pick up that round almost immediately after it reaches its rearmost position and starts forward. If an over speed bolt cuts the time available for a magazine to push the next round up too much, you can absolutely have a bolt over base failure to feed.

With potentially iffy x39 magazine geometry in play, OP can be even more likely to have an issue with the system by increasing the bolt speed. Luckily since the rifle worked fine without the can, the OP should be able to regulate the gas down to decrease the impulse on the BCG, or increase the buffer weight to add to the total mass and slow the stem (obviously increasing spring rate could help too). I prefer to just use an adjustable gas block over going very heavy on buffers, leaving medium buffers in for a smoother shooting experience. It's certainly easier to swap in buffers to see if you can get the system timing back in sync, or if you don't want to use AGBs for some reason.

 

[TonyAngel]

Just to be clear, the bottomline is that the closed bolt lock time needs to be increased. You can do this by either turning down the gas with an adjustable gas block or a heavier buffer. In some situations, an adjustable gas block is necessary.

A heavier spring can help with bolt velocity, but has very little effect on closed bolt lock time.

X39 setups are a finicky PITA.

 

[charger23]

A flow through suppressor like Huxwrks Flow 7.62 would eliminate your issue as well if buying another can is a consideration. If it’s no problems unsuppressed, then a Flow can wouldn’t cause any additional back pressure, or a negligible amount at most.

 

[mtrmn]

... X39 setups are a finicky PITA.

THIS

 

[TonyAngel]

A flow through suppressor like Huxwrks Flow 7.62 would eliminate your issue as well if buying another can is a consideration. If it’s no problems unsuppressed, then a Flow can wouldn’t cause any additional back pressure, or a negligible amount at most.

I agree with this. Typically, the "smart" thing to do is to tune for a happy middle ground between shooting suppressed subs and unsuppressed supers. Since subsonic 7.62x39 is about as common as chicken teeth, you'll likely run supers suppressed and unsuppressed. This is a pain in the butt with a high back pressure can, usually leaving you a bit undergassed with unsuppressed and a bit overgassed when suppressed. This is when an adjustable gas block can save the day. Either that or keep a couple of buffers on hand.

Going with a low pressure can, like a Hux, will make your life easier. It isn't the best at suppression, but still a lot less loud than without it and, as youtuber Hop put it, it doesn't make your gun shoot worse.

 

[mettee]

But if you already have a specific can sometimes the cost is prohibitive to get another that is flow through.

 

[Kickin45]

Do some reading and research on suppressing a gas operated rifle!

 

[Gtscotty]

But if you already have a specific can sometimes the cost is prohibitive to get another that is flow through.

In that situation, what I've done is tune the rifle to run optimally suppressed and run it suppressed all the time. I'd assume the OP isn't using a x39 AR as a go to war type rifle, but rather for hunting or something like that. I also like SA bleed off gas blocks, in my experience it's been easier to find a setting that runs well both unsuppressed and suppressed as long as the can isn't super high back pressure.

I do have my first two low back pressure cans now though, and they do make things easier, but they aren't mandatory.

 

[mettee]

I just brought that up, because its not realistic to tell someone to "just go get a flow through" in most circumstances.

 

[charger23]

Just a suggestion as it is viable solution although costly. At least now it’s also not a year turnaround. I got one approved a month ago in 2 days on trust. For some it’s not necessarily a money issue. They just want their shit to work. I run a Flow 762 on a 11.5” sig 7.62x39 and it suppresses better than expected. YMMV. Having a flow through can for anything semi auto is gonna be advantageous.
Or, you can chase the problem with adjustable gas blocks, buffer weights, etc. still costs money and time. Time is money.

 

[TonyAngel]

If you dont want to mess with adjustable gas blocks or a lot of tuning mess and you know how to replace a gas block, I'd get a yankee hill suppressor gas block. It comes with an undersized gas port. Then you can drill it out to what ever size you want.

With your 16" barrel, assuming carbine length gas, maybe start with a .060 gas port size and work your way up from there.

I use a lot of the yhm gas blocks. They're cheap. Like $20. A lot cheaper than a BRT gas tube.