Topic: Military Brass

[monkeywrench]

This question is somewhat related to my other question. When loading once fired military brass such as L.C., how much should I reduce the starting load by? I loaded some L.C. brass although not at the starting load recipe, it was not anywhere near the maximum either. I shot on a hot day and had some pierced primers. This problem ate the firing pin in my AR. I do not wish to go thru that again. Thanks for any help.

[Jeff]

You can always weight both cases and then fill with water and weigh again.  That should give you an idea how the case capacity differs.  I don't know how much difference is a lot but I've seen that posted on snipershide.  I'm sure a little research would answer the question.

BTW, I have the same question but don't have the complete answer yet. 

[High Wall]

You can compare cases just by weighing them.  If they are clean, the primer knocked out, and trimmed to the same length, any variation in weight will tell you which has less interior volume.  You can weigh brass from a known lot that you have used for loads that were OK for pressure.  I usually get an average of 10.  Then weigh the new brass.  If the new stuff is a lot heavier, interior volume is going to be less.  Everything else being equal, that heavier brass will give higher pressures, so it may be prudent to back off a little, check, then work back up if appropriate.

With 5.56 brass, I've found that military brass is not always heavier than commercial .223 brass.  Military 30-06 and .308 brass always is heavier than commercial in my experience.  45 ACP brass is all over the map. 

[monkeywrench]

Digging into this a little deeper. First I weighed the Win brass, empty 97.8 grains.
                                                                     L.C. brass, empty 94.1 grains.
                                             Filled with water  Win brass,         128.1 grains.
                                             Filled with water L.C. brass,          125.3 grains.
So if I figure correctly, L.C. brass has approximately 2.2% less volume than Win brass, and weighs approx. 4% less than Win brass. Am I figuring that correctly? Should I reduce the starting load by 2.2% ? I kind of figured that the L.C. brass might be heavier due to thicker walls or web, but it is lighter. Perhaps a different alloy composition, or density?
                                                                   

[Spiff]

I would vote for composition of the brass being a factor.

If the brass has been sized and trimmed, how much brass was removed from each case during this process?

LC brass, coming from a military load, may have/should have stretched more, and therefore had more trimmed off of it than the Winchester brass. This would explain the lighter weight.

If your trimming brass, the brass is coming from somewhere and that "somewhere" is usually the case wall or neck/shoulder area. Thinning them out. Which you would think would cause an increase in volume (as well as case separation and/or neck splitting on down the road).

Because there doesn't seem to be a correlation between thinner brass on the one hand and less volume in the other, the explanation would seem to lie elsewhere, i.e., brass composition.

As far as your original question goes, the answer is pretty straight forward. If the case is showing pressure signs, back off the powder charge, or use a powder that is less temp sensitive. Remember, all firearms are different. That is why you should always treat the reloading books as a reference only. I fell into this trap myself, I got a .308 load of 44.5 grains of Reloader 15, using a 175 SMK off of sniper's hide. Although the load performed well numbers wise (SD of ~9, and fps ~2700) I was getting smashed and cratered primers. Some of the cratered primers were just this side of the ragged edge of being pierced.   

[pv74]

I just work up loads separately for .mil brass.

Published starting loads should be safe.
Like was said before, back off if starting to see pressure signs.