Commercial vs. Military .223/5.56mm Cases

[Gary L. Griffiths]

There is a thread over on THR about case capacity/weight of commercial vs military .223/5.56mm cases, so just for gits and shiggles, I spent a rainy yesterday morning doing some weighing and measuring. From my reloading bench, I selected lots of 5 cases each of resized, trimmed and primed brass from Federal, PMC Bronze, PPU Match, and PMC X-Tac as well as 5 unfired primed Lake City 13 cases. First, I measured case capacity using some BLC(2) powder by filling the case to overflowing, then leveling the mouth with the edge of my scales powder pan. I poured each charge into the pan and weighed them with the following average weights (in grains):

Federal, 30.84, SD 0.30; PMC Bronze, 30.95, SD 0.37; PPU Match, 30.30, SD 0.31; PMC X-Tac, 30.19, SD 0.41; Lake City 30.16, SD 0.61.

Primed case weights: Federal, 96.12, SD 0.48; PMC Bronze, 96.46, SD 0.13; PPU Match, 98.17, SD 1.06; PMC X-Tac, 96.40, SD 0.49; Lake City 96.10*, SD 0.52. *Adjusted for weight difference of 0.2 gr. between CCI 400 and CCI 41 primers.

Case lengths: Federal, 1.7497", SD 0.0055; PMC Bronze, 1.7554", SD 0.0023; PPU Match, 1.7540", SD 0.0031; PMC X-Tac, 1.7540", SD 0.0022; Lake City, 1.7538; SD 0.0007.

Correlation of case weight to case capacity: Federal -0.51; PMC Bronze -0.06; PPU Match +0.44; PMC X-Tac -0.68, Lake City -0.42.

Bottom Line: Lake City cases don't have significantly less capacity than commercial cases, and there is no real correlation between case weight and capacity.

FWIW

 

[steve4102]

Bottom Line: Lake City cases don't have significantly less capacity than commercial cases, and there is no real correlation between case weight and capacity.

There ya go, been saying this for a long time, yet there are still many non-believers.

That said, I'm not a fan of testing Case capacity with Powder, I use H20.

 

[Gary L. Griffiths]

Addendum

It occurred to me that I was kind of comparing apples with oranges in comparing fired and resized commercial brass against unfired military brass. This morning, I resized, trimmed, and primed five fired Lake City 13 cases and measured them as I did the commercial cases Saturday. Results were, avg capacity 30.84 gr, SD 0.50; case wt avg 95.81 gr, SD 0.58, and avg length 1.7661, SD 0.48. There was a +0.52 correlation between case weight and capacity which pretty well shoots down any notion of using case weight as a predictor of capacity.

The idea that military cases are thicker and therefore have less capacity than civilian cases is also suspect, in that the fired LC cases had an average capacity exactly equaling the Federal cases I tested Saturday, which proved to have the second highest capacity of any of the brands I tested.