Case shrinkage - more data

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Case shrinkage - more data

Post by Aprilian on 2/5/2017, 12:00 pm

A while ago, I posted a link to some great articles at Mass Reloading including this one on case shrinkage. http://massreloading.com/loading45ACP.html

This morning I decided to do an experiment and find out how much the sizing, flaring and bullet insertion contributed to the shrinking of the case at the base.

I took 4 brand new IMI Match cases with identical .8930 lengths and planned out
#1 - 30 size and flair 30 times + 1 final sizing
#2 - 30 size, flair and bullet insertion + 1 final sizing
#3 - 30 size, flair, insert, crimp + 1 final sizing
#4 - control 

What I found in test 1 and 2 allowed me to skip the 120 die changes which would have been required for test #3
#1 - final length - grew to .8955
#2 - final length - grew to .8975
#4 - still .8930

So working the brass without shooting it can actually lengthen your brass if you want it to be slightly longer to match your chamber.  Not at all what I expected to find.  The most resistance (on single-stage press arm) came from resizing, so perhaps that is the most important contributor to this lengthening of the brass.

I don't plan to do anything different in my loading with this info, I just found it interesting enough to add to the knowledge base.
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Re: Case shrinkage - more data

Post by Jon Eulette on 2/5/2017, 12:16 pm

So go shoot them and tell us how much they shrink? ;l)
Jon
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Re: Case shrinkage - more data

Post by DavidR on 2/5/2017, 6:49 pm

Generly a 45 acp  doesn't shrink or grow enough to make any difference in our sport
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Re: Case shrinkage - more data

Post by willnewton on 2/5/2017, 7:36 pm

You are essentially doing a miniature extrusion at the case mouth with all that thinning (flare) and compression (sizing).  The metal is trapped on all sides but the top so it goes up and the case gets longer.

You have also just work hardened the crap out of those case rims and I would just make some dummy rounds from them so they don't circulate in your regular ammo.

Since you got me thinking, I measured my old much-reloaded cases vs. newer reloaded cases vs. unfired Starlines.  In the random selection of several cases I only found about .004" difference in length.  Also the shortening happens where the case necks in to accept the extractor, but before the base.  Does it matter to your score?  My recent testing shows that it seems to matter only for my cases when you AND the gun can shoot at the highest level possible already, then look at your cases, but you are probably sponsored by then anyway, so uh, yeah.  Smile
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