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New Brass Case Length

941 Views 2 Replies 2 Participants Last post by  liver
I believe specs for 10mm brass length is .992. I just checked 20 out of a new bag of 100 Winchester and low was .981 and hi .988 with average .984. So I reload for a OAL of 1.258 - .260, does case length matter? Should I trim to the average for better reliability? or let the case expand to .992, again does it matter or am I just chaseing my tail? :dog:
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The only problem this will cause is if you crimp, you will get some inconsistencies in amount of crimp. As long as the bullet seating depth (i.e., OAL) is consistent, it won't significantly affect your velocities/pressures one way or the other, but a varying amount of crimp can. If you want to have consistent crimps, then trim them all to the same length.

I try to run my brass as close to .992 as I can (just a personal preference), so if it was my brass, I would leave it alone. With the exception of the 135gr bullets, I only "crimp" enough to remove the flaring on the case mouth for positive feeding, which is really not a crimp at all. Again, this is just my personal preference. There is plenty of documented data that shows a heavy crimp can increase velocity and reduce your velocity spread, while others claim that they see very little difference, and still others seem to think a heavy crimp that leaves a large indentation in the bullet reduces the accuracy of the load.
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Thanks for the crimping info. I believe I will trim my hotter carry loads to an average length and not worry to much about my everyday shooting loads. I've built up a Longshot load with Hornady 200 HP/XTP's that I really like (ave. 1125 - es. 34.35 - sd. 9.21) uniform case and OAL length should make this a reliable load.
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