Military Case Loads

jbmoose

I understand that when reloading military cases, I should reduce my loads because of the thicker case walls. However, I have been told to reduce my loads anywhere from 10% to 2%. This is too broad a range for me to be comfortable with. I thought I would ask the Forum. Is there a good informed consensus out there? Also, as far as reducing loads, does it make a difference if I am loading small rifle, large rifle or pistol military cases or is the reduction the same for all? Does it make a difference if I am loading LC or WCC?

JustC

OK,..do this

Take the old brass you were using and the military brass you want to load. Size them both in the die to make sure their dimensions are the same.

Now weigh the old case empty, and fill with water to the top and weigh again. Do the match and you'll have an internal volume in grains.

Repeat this step with the military brass and get the internal volume of that brass in grains.

Now, again, divide the military volume (smaller volume) by the commercial brass volume, and you will end up with a percent. Let's say the division gives you a .93 on your calculator,..this means the military brass has 93% of the volume of the commercial brass,...or in other words, it has a 7% LESS volume. Sooooo, take your load from the current commercial brass, and reduce it 7% (by multiplying by .93) and this will be a very close starting point for the new load in the military brass. Within a load or two in both directions (+/-) you will have the new accuracy load in the new case.

Ambrose

JustC; I like your method. But do you think comparing case weight would sufice? I just weighed a R-P .223 case @ 95.9 gr. and a WCC 5.56 case @ 96.7 gr. (I was surprised that the difference was so slight). Since the difference is eight/tenths of a per cent, couldn't the WCC load just be reduced by 1% and be good to go? Weighing cases is easier, faster, and less messy than the water method. Do you think it would work as well?

JustC

Ambrose,...I think it may be close, but brass metalurgy can be different from one manufacturer to another, as well as lot-to-lot, which can result in different densities of the surrounding metal. I admit that is splitting hairs,...

IMHO the best way to compare case to case, is the internal volume, after sizing. The sizing step uniforms the external dimensions for both makes of brass. Therefor, the only dimensional variances will be in the internal area of the case body. The water test, while crude, is pretty accurate most of the time.[;)]

Ambrose

JustC, I agree that your water method will be more precise. But I think I'll try an experiment with my method. I'll scrounge around to see if I can find some brass with a greater than 1% difference in weight and reduce the powder charge accordingly. I'll choose a less than max. load, assemble both sets of cases with identical components, and fire them across the chronograph screens under the same conditions. If the results look interesting, maybe I'll post them here. (It's always good to have another excuse to shoot the guns!)

JustC

let us know the results.

Damn, now I wanna go shooting[:p]

Ambrose

OK, I'm kind of laid up today, anyway, so I dug through my old notes. Turns out I did that experiment with a .223 on 8/18/93 (inadvertently). I still have those cases from that experiment. I won't mention the load since it was NOT a mild one. I fired 10 five-shot groups on that day--5 with FC cases and 5 with cases headstamped Winchester. I used the same powder charge for all 50 shots. The rifle (if it matters) is a heavy barreled Sako with a 12X Leupold. The rig generally averages .8" to .9" with full-power loads. Results as follows:

With FC cases: ave.=3265 fps; ave. group size=.93"
With Winchester cases: ave.=3276 fps; ave. group size=1.02"

To apply that experiment to this question, today I weighed a sample of each of those fired cases. Five FC cases averaged 95.1 gr. with 1.3 gr. difference between heavyest and lightest. Five Winchester cases averaged 96.8 gr. with 2.7 gr. difference. So the Winchesters were 1.8% heavier than the Federals and yet the velocity difference was only 11 fps! I would have expected something on the order of 60 fps. Of course I have no way to measure pressure but pressure generally follows velocity until you get really over the top.

While I was at it, I weighed a sample of LC-83 brass: 95.3 gr. with 2.1 gr difference. So military brass is lighter than at least one brand of commercial brass.

I guess the conclusion I came to is to weigh your brass. If the difference is slight, treat it like the stuff you've been using. If more than slight, use JustC's water method and adjust your loads accordingly. The other conclusion: Save your old records, they might come in handy some day.

I would hope that whoever reads this would draw their own conclusions.

Ambrose