I had a partial case head separation using a 1.8oz buffer

[stonehog]

I wrote a section on this in Volume I of the 6.5 Grendel Handbooks back in 2012-2013, pages 19-21.

The section is titled: Barrel length and gas system length configurations.

“Some shooters who have run certain hand loads through a 20” rifle with rifle-length gas, have then taken those same loads to see how they do in a 24” or even 28” rifle with rifle-length gas, and experienced apparent extreme pressure signs, where brass begins to separate at the head/web junction with the case walls just above the extractor groove location (See Figure 10).”

This is what cases look like when you have too early extraction:



You can run that load through the 20” RLGS and brass comes out without these bulges.

Put the exact same load into 28” RLGS and you will see this problem.

It’s a cyclic rate problem.

You can load a hotter load in the 20” RLGS and not even see this happen, use a reduced load in the 28” RLGS with the same components and it will still be there.

It’s not the brass’s fault, but the cyclic rate due to port location, plug dwell time, and carrier/buffer mass not able to resist the imparted inertia.

Cyclic rate timing is essential to master on any gas-operated firearm. The AR-15 does quite a good job of it when everything is balanced with port location, port size, plug dwell time, carrier mass, action spring weight, and buffer mass relative to the propellant mass, bore volume, projectile mass, working pressure, and propellant burn rate.

Think of it as a teeter-totter. On one end is the pressure-containment vessel and gas system, while on the other end are the reciprocating masses and spring.

The fulcrum is the bolt lock-up.

If you out-run the ability of the reciprocating mass and locking system to keep the case locked in the chamber until pressure subsides, you will have expanded case heads, partial or full case head separations, failure to extracts, torn case rims, etc.

Timing of the unlocking cycle is essential to avoid this.

OP used a 1.8oz buffer with CLGS, and dropped one end of the teeter-totter on the ground.

That’s a perfect recipe for partial case head separation.

LRRPF52 - I really appreciate all the work you (and the others as well!) have put into this thread. I've learned more about the Grendel and ARs in general from this thread than anything I have seen on YouTube or read. This forum is a real gem! Thanks for all the time you put into this - I know it was a lot! I just ordered one of those awesome boonie hats to show some appreciation!

Stonehog (Brian)