Overgassed AR-15

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Overgassed AR-15

Postby Georgezilla » Sun May 25, 2014 10:03 pm

My personally built AR-15 blew a primer which somehow got lodged behind the cam pin while the rifle was IN battery...that had to have been a one in several million. At the time, I didn't know that's what happen so I soaked the whole upper in penetrating oil to deactivate the primer if there was a stuck round, then tried to pull off the barrel. Obviously the bolt could not rotate in the carrier because of the stuck primer, so I was unable to remove the barrel. The eventual solution was to use a wooden dowel and a mallet on the carrier side of the BCG to and force the bolt to rotate by deforming the primer.

This all happen with Independence 5.56 ammo which isn't known for its quality. However, the cases fired from the firearm in general displayed signs of over pressure. Federal XM855s displayed significant signs of over pressure -- flattened primers, flattened head stamps, ejector smearing. The relevant specs of the firearm are: 16" 5.56 barrel (BCM), mid-length gas, M16 BCG (BCM), 2.9oz buffer.

Because I was using the same manufacturer for the barrel and BCG, I only got a field gauge to test the headspace. The rifle passed the field gauge test. I ended up swapping the BCM BCG for another one which also passed the field gauge. With the new BCG, I was still getting some pressure signs, but based my knowledge they are on the upper end of acceptable. Is there anything else that you guys would recommend to tone the gas in this rifle down a little? I would like to bring the pressure signs from barely acceptable to very acceptable.


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Postby charlesb » Mon May 26, 2014 5:39 pm

I'd try it with different ammunition before I tried anything else.

Sounds like you got a bad lot of ammo, or some Bubba reloads passed off as factory stuff.

Too much gas would not deform the headstamp or flatten primers, but too hot a load sure would.

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