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Old June 23, 2011, 09:37 PM   #15
Slamfire
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Join Date: May 27, 2007
Posts: 4,046
I have been developing loads with lubricated cases for at least a decade now.

I noticed that when I shot lubricated cases in my M1a's, I got rounded primers. Dry cases gave me flattened primers. Obviously combustion pressure is the same, so I figured out that with lubricated cases, the case and the primer slide back to the bolt face at the same time.

So, I started using lubricated cases in load development. When primers start flattening for real, I know pressure is going up.

Primer flattening is just one indication of pressure and unfortunately it is an unreliable indicator.

Positive indications of too much pressure are leaking primers, blown primers, sticky bolt lift, and brass flow into the bolt face. If you get these signs you have exceeded safe operating pressures. Brass flow around the firing pin is not always a positive indication as one manufacturer has redesigned their rifle to do this. Apparently it provides a better gas seal around the firing pin. Since I also use a chronograph in developing loads, I believe that if my loads exceed published velocity values, regardless of primer or bolt lift, then I am exceeding reasonable pressures.

If your brass ever looks like this, it is way too hot!

These rounds were fired in .223 service rifles at Camp Perry. They have all the indications of excessive pressures. Except for bolt lift. AR's extract ammo without any assistance from the operator.

AMU long range brass.


USMC Rifle Team long range brass

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