(I'm having a discussion with someone regarding thickness variations between commercial and military brass, and thus... this repost.)
is in the process of load development for Liberty, the M1 Garand. This
entails shooting... lots and lots of shooting... but that's only part
of the happiness. It also requires lots of hours blissfully spent at
the reloading bench.
Part of the process involves case
preparation. On this topic, books have been written... but not by The
Fat Man. Here, just one small topic is being addressed.
choosing which cases to run the load development with, the entire 30-06
inventory in play. That means over 1000 cases of different date and
manufacture. Amongst them, a fair number of military casings.
thing is, there is a 'Given' in the reloading world. It's been
engraved in stone for so many generations that it's accepted as a golden
rule. That is: Military brass is thicker and heavier than commercial
brass. That means the interior volume of the case is smaller, so
therefor the charge weight must be lowered or excessive pressures will
But.... is this rule so golden?
took a bullet for the team, and weighed several hundred cases, both
commercial and military. The results were unexpected. Weighing the
cases is a traditional way of separating out cases into lots of
like-volume. The theory being that all sized cases have outside
dimensions pretty much the same, so any weight variations must point
towards differing case thickness, and thus differing internal volume. (As
one intelligent reader pointed out to The Fat Man... metal density
comes into play as well. He proposed a simple test for internal volume,
consisting of filling the cases with water before weighing them. This
makes sense, as the weight on the water filling the case will vary
depending on internal volume of the case. This sounds like a wonderful
excuse for further testing, and another article here....)
The bulk of the cases were divided into three major types. Greek HXP, Lake City, and Commercial Remington and/or Federal.
the unusual part.... on average, the commercial brass was heavier than
all the military. Both Lake City and the commercial were heavier than
the Greek HXP military. This indicates the HXP does not have a smaller
internal volume, but in fact has a larger one. This changes the whole
ball game when loading with the Greek HXP brass.
That chart below shows a clearer picture of what was found:
I know this isn't exactly going to be wildly interesting for those not
deep into the intricacies of hand loading.... but for those us who share
that particular addiction, it's fascinating.
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