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Discussion Starter · #1 ·
I have a M16 which I originally had a 14.5" barrel on it with a full auto BCM bolt carrier group in it. When I swapped out the barrel to 11.5" I noticed that the gas rings on the bolt failed the field test of supporting the weight of the carrier... I can do into more detail on this if you don't know what I am talking about. In any case I did not think this was a big deal because I had put around 3000 rounds though the barrel and figured it was time to replace the rings which I did. Once I replaced the rings and inspected the bolt, everything looked good so I decided to reuse the bolt carrier with the new barrel. Went out and put some rounds through it using a T2 buffer from Spikes. The gun was acting like it was over gassed and tossing the brass to the one o'clock position. Next I replaced the buffer with a T3, this fixed the issue and brought the shell casing back to ejecting at the 3 to 4 o'clock position. The gun also did not suffer from anymore bolt bounce and I could dump a full mag with no light primer strikes. I could not do that prior with the T2 with the 11.5, it would light strike 2 to 3 times per 30 rounds. With the 14.5 barrel I did run the T2 with 0 issues.

Sooooooo... I am now happy with the way the gun is working but here is the thing... I was cleaning the gun again tonight and after less than 500 rounds, the gas rings on the bolt is back to failing the field test again. Is this because the gun is over gassing? Is this a problem if I run the gun like this? Not sure if I have an issue or not... Looking for advice from possible other M16/ AR15 full auto owners.

Thanks!
 

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Discussion Starter · #3 ·
I have had McFarland continuous gas rings in all of mine since the 90s and never had a gas ring problem in 35-40K rounds on 4 different guns.

View attachment 33128
Hmmmm... I wonder if trying something like these would be a good solution. Wondering if the gun is over gassing with the shorter barrel and causing the rings to blow out. I mean visually, they look fine but they fail the field test so I am not sure if saying they are "blown out" is the correct way of putting it.
 

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Hmmmm... I wonder if trying something like these would be a good solution. Wondering if the gun is over gassing with the shorter barrel and causing the rings to blow out. I mean visually, they look fine but they fail the field test so I am not sure if saying they are "blown out" is the correct way of putting it.
Short guns are usually undergassed or underpressured because someone tried to fix their undergassing problem with drilling larger and larger holes until their previous improvements are ruined.

Have you tried running a regular M4 buffer to see how it runs? If it's not throwing your brass 20 feet then you're definitely not overgassed.
 

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Discussion Starter · #5 ·
Short guns are usually undergassed or underpressured because someone tried to fix their undergassing problem with drilling larger and larger holes until their previous improvements are ruined.

Have you tried running a regular M4 buffer to see how it runs? If it's not throwing your brass 20 feet then you're definitely not overgassed.
The gun runs great with the T3 buffer, light primer strikes with the T2. I have a regular buffer weight but I have not tried that. I have honestly heard the opposite that on shorter barrels the gas port is drilled bigger to fix any sort of the cycling issues. I don't think the gun is under gassed because on the weakest 223 ammo I have, the bolt always holds open on the last shot with the heaviest (T3) buffer I own.
 

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Try the McFarland one piece ring.

Thought about going to a piston retrofit kit, like Adams Arms??? Keep the gas out of the reciever which will make it cleaner, and cooler.
 
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The gun runs great with the T3 buffer, light primer strikes with the T2. I have a regular buffer weight but I have not tried that. I have honestly heard the opposite that on shorter barrels the gas port is drilled bigger to fix any sort of the cycling issues. I don't think the gun is under gassed because on the weakest 223 ammo I have, the bolt always holds open on the last shot with the heaviest (T3) buffer I own.
Yeah, you do drill the gas port bigger to make up for the lack of bore forward of the gas port but at least on a 10" you can go too far and the pressure drops because the impulse is too short and the hole too big. Now that I think about it an 11.5 should have enough barrel ahead of the port to not have that happen but the most common sources of problems on these guns are "dwell time" and "bolt bounce" which is why these various buffer weights were created in the first place.

You've tried every buffer and adding mass to the system seems to help but your gas rings are blowing out so my next question is...

How far is this gun throwing brass and where is it landing?
ARejectionpattern.jpg
 

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I'm having a similar issue although mine is semi-auto but does have a full auto BCG, both from BCM and Sabre Defence.

The BCM is brand new and I haven't gotten to shoot with it yet.

The Sabre Defence BCG had less than 700 rounds through it on a 16" barrel with mid-length gas and this happened.
image.jpg

I then ordered a new BCM BCG, new barrel chambered in .223 Wylde with carbine gas (found out I had mid-length after I tried installing the new barrel and my gas tube wouldn't fit), new heavy buffer 4.9 oz and a Spikes Tactical Dynacomp Extreme 2 muzzle break.

I used to run my AR on the dry side (oiled but wiped down) and seeing how I had mid-length gas before I'm thinking mine happened because it wasn't wet enough. I'm going to try running the new BCG really wet this time and see how it works out.

Ill also keep keep an eye on my brass to see of I'm now over gassed with carbine gas vs mid-length on the same 16" barrel.
 

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Discussion Starter · #9 ·
Yeah, you do drill the gas port bigger to make up for the lack of bore forward of the gas port but at least on a 10" you can go too far and the pressure drops because the impulse is too short and the hole too big. Now that I think about it an 11.5 should have enough barrel ahead of the port to not have that happen but the most common sources of problems on these guns are "dwell time" and "bolt bounce" which is why these various buffer weights were created in the first place.

You've tried every buffer and adding mass to the system seems to help but your gas rings are blowing out so my next question is...

How far is this gun throwing brass and where is it landing?
View attachment 33140
With the T2 they where ejecting at the 1 o'clock position (over gassing), with the T3 the 3 to 4 o'clock position. The bolt locked open on every round even with the T3 and the weakest 223 I had. To me... That does not sound like too little of gas. Bolt bounce with the T2, none with the T3.
 

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Discussion Starter · #10 · (Edited)
I'm having a similar issue although mine is semi-auto but does have a full auto BCG, both from BCM and Sabre Defence.

The BCM is brand new and I haven't gotten to shoot with it yet.

The Sabre Defence BCG had less than 700 rounds through it on a 16" barrel with mid-length gas and this happened.
View attachment 33141

I then ordered a new BCM BCG, new barrel chambered in .223 Wylde with carbine gas (found out I had mid-length after I tried installing the new barrel and my gas tube wouldn't fit), new heavy buffer 4.9 oz and a Spikes Tactical Dynacomp Extreme 2 muzzle break.

I used to run my AR on the dry side (oiled but wiped down) and seeing how I had mid-length gas before I'm thinking mine happened because it wasn't wet enough. I'm going to try running the new BCG really wet this time and see how it works out.

Ill also keep keep an eye on my brass to see of I'm now over gassed with carbine gas vs mid-length on the same 16" barrel.
My gas rings don't look anything like that, they actually look 100% normal. They are just failing support the weight of the carrier when testing. They just seem to have little resistance in the carrier.

I run my guns on the dry side as well, hell I never even oil the rings... Maybe that is part of the problem?
 
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