Got Gas? - Overgassed AR problems

[DocJekyll]

Hello INGO,

I recently, and finally, got to shoot my 10in 300blk SBR at the range. I've got to say I really did enjoy putting some rounds down range with it. There is however one problem... I didn't get any pictures of it, however I've identified that it seems to be severely overgassed. Here are the symptoms I noticed:

1. Dented Brass: The open end of the brass was dented from having hit the brass deflector with great force. This was consistent among several mags as I fed them through.
2. The Ejector: The ejector is leaving indentations on the back of the brass.
3. Extractor: The round is being so forcefully removed from the chamber that it is actually bending the rim on the case head. In one case with Hornady, It was actually so bad it pulled the primer out of the case.
4. Inconsistent ejection pattern: I've noticed that the ejection pattern is sometimes very far forward, or extremely far backward.

The gun feels a lot heavier recoil than I would expect for something running a muzzle brake. What kinds of options do I have for reducing the gas? Right now I've got a BCM gas block and pistol length tube on the 10in barrel currently.

[video]https://youtu.be/t_usVFbc8D8[/video]

 

[MontereyC6]

What buffer are you using?

 

[Tanfodude]

A heavier Buffer and the more coil recoil spring should manage that, it's supposed to be ejecting brass @ 3:00.

 

[DocJekyll]

What buffer are you using?

The buffer is built in to the bolt carrier. I'm worried it's unlocking before the pressure has sufficiently reduced enough for it to operate properly.

Its currently ejecting anywhere between 3:00 and 5:00 now and is not very consistent.

 

[MontereyC6]

Which bcg are you using then? Something isn't adding up, and I'm thinking it's on the buffer end, not the gas port.

 

[M67]

Which bcg are you using then? Something isn't adding up, and I'm thinking it's on the buffer end, not the gas port.

It's A PDW style stock

 

[DocJekyll]

It's A PDW style stock

This exactly. From what I understand of it, while slightly important for tuning, the buffer and spring will tend to cover up over gassing issues more than solve them. I will say though that I feel like the spring is pretty light on the Troy PDW stock. Because the buffer is built in to the carrier, I can't change that. I may look at whether it's possible to add weight inside the buffer though. I haven't looked, but I believe that the spring is also shorter than a standard spring. The only other option I can think of is a tunable gas block.

I have a Saker 762 on the way and know that the overgassing issues will increase when suppressed.

 

[M67]

This exactly. From what I understand of it, while slightly important for tuning, the buffer and spring will tend to cover up over gassing issues more than solve them. I will say though that I feel like the spring is pretty light on the Troy PDW stock. Because the buffer is built in to the carrier, I can't change that. I may look at whether it's possible to add weight inside the buffer though. I haven't looked, but I believe that the spring is also shorter than a standard spring. The only other option I can think of is a tunable gas block.

I have a Saker 762 on the way and know that the overgassing issues will increase when suppressed.

I'll probably get an adjustable gas block for my 8.5" as well, mine is consistent in ejecting brass, but the necks get deformed from hitting the shell deflector so hard, so much I put some grip tape on it to cushion them a little. I'm only shooting 10.5gr of 4198 with a 180gr bullet and using a 762 Saker as well and tried a H2 buffer in it yesterday and still did it.

As for adding weight to the BCG, maybe they used a steel core and you can put tungsten in it to weight it down, but with the price of tungsten, the adjustable gas block would probably be a good option

 

[DocJekyll]

I'll probably get an adjustable gas block for my 8.5" as well, mine is consistent in ejecting brass, but the necks get deformed from hitting the shell deflector so hard, so much I put some grip tape on it to cushion them a little. I'm only shooting 10.5gr of 4198 with a 180gr bullet and using a 762 Saker as well and tried a H2 buffer in it yesterday and still did it.

As for adding weight to the BCG, maybe they used a steel core and you can put tungsten in it to weight it down, but with the price of tungsten, the adjustable gas block would probably be a good option

I'm wondering if having the longer barrel on the 300blk (A 10in over a 8.5) is increasing the time and pressure in the tube because the dwell time is longer? This build has been only the second time I've really looked at tuning a rifle so I'm still fairly new at it. Perhaps a shorter gas pulse would reduce the gas. Hmmmmm.....

 

[sig1473]

Manufacturer of the barrel? I didn't see that listed.

 

[DocJekyll]

Manufacturer of the barrel? I didn't see that listed.

It's a Lother Walther through Spikes.

 

[rvb]

2. The Ejector: The ejector is leaving indentations on the back of the brass.
3. Extractor: The round is being so forcefully removed from the chamber that it is actually bending the rim on the case head. In one case with Hornady, It was actually so bad it pulled the primer out of the case.
4. Inconsistent ejection pattern: I've noticed that the ejection pattern is sometimes very far forward, or extremely far backward.

The gun feels a lot heavier recoil than I would expect for something running a muzzle brake. What kinds of options do I have for reducing the gas? Right now I've got a BCM gas block and pistol length tube on the 10in barrel currently.

factory ammo or reloads? the above signs (esp the ejector damage to the brass) sounds more like hot ammo vs just too much gas. brass flowing into ejector hole?

pic of brass?

-rvb

 

[CountryBoy19]

factory ammo or reloads? the above signs (esp the ejector damage to the brass) sounds more like hot ammo vs just too much gas. brass flowing into ejector hole?

pic of brass?

-rvb

I was going to post the exact same info.

Your symptoms are a LOT more like hot ammo vs. over-gassed gun.

FWIW, over-gassing an AR should not make it eject the brass any harder, the brass is ejected by a spring/plunger that has a consistent force no matter how much gas pressure there is. It may change where the brass lands etc, but it shouldn't be the cause of dented case-mouths. Dented case-mouths could just be part of the game (a small dent is normal in quite a few cases and is removed with resizing).

The most tell-tale sign is the brass-flow into the ejector hole. There is NO POSSIBLE WAY for that to happen outside of over-pressure or soft brass.

The brass-flow into the extractor could be hard extraction, overpressure, or a result of the fact that you're likely running a pistol length gas system which can potentially begin extraction before the pressure in the barrel has dropped enough to free the brass from the chamber. To check for this you need to look closely at the rim where it is deformed. Are there deep cut/pull marks from the extractor? Some light marks are normal, even very slight deformation isn't unusual, but deep pull marks would indicate a gas timing issue.

 

[david890]

I have a Paladin Machine adjustable gas block on my 16" rifle, and I generally run with it fully open (100%/60%/Off). Very low report with the AAC Cyclone suppressor mounted, and recoil is negligible. My only complaint about the PM gas block is that the stem to adjust the setting isn't 1"-2" long so that it protrudes from the foreguard.

Got that can for my .308 bolt-action, but with 3 discs in my neck fused, it hurt too much to shoot. Having the 300 Blackout as my 7.62-caliber firearm was a good choice (built about 3 years ago).

 

[DocJekyll]

Just a quick update. I went back out to the range and put about 500rds out and haven't had the same issues. It's possible the factory box I had was slightly over powdered. I haven't gotten into reloading and haven't used reloads in the rifle yet. I'm leaning to thinking maybe I just had a really hot box or Hornady 110gr Vmax 300blk ammo. I tried a couple of different manufacturers of ammo and haven't had the same issue. I am really liking the 120gr OTM Supersonic from Remington though. Very consistent and not super expensive.

Thanks all.