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Old June 18, 2011, 09:28 AM   #7
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 10,250
Thanks for the link. I've got Zediker's book and had read that information awhile back, but it's good to have something to refer others to when they can't get to a copy of the book. I'm glad Zediker put that up to share.

I should point out that one difference I've found from Zediker's data is that the IMI Match brass I have is around 186 grains, which is about six grains heavier than the LC match brass I have. The rule of thumb I use in the .308 is to divide the case weight difference by 14 to get the approximate number of grains powder charge difference I am likely to end up with for a given barrel time. So, about 0.5 grains less powder in the IMI Match than in my LC for the cases I have. That would be with Reloader 15, which is what the military puts in M118LR these days.

BTW, that formula assumes the head diameters are the same so that weight difference equals water capacity difference times 8.53. If they don't match, you have to weigh the filled water capacity of the two .308 cases you are trying to compare, and divide the difference by 1.7 to get an estimate of the change in charge that will keep barrel time constant.
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Last edited by Unclenick; June 18, 2011 at 11:56 AM.
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