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Old November 30, 2009, 02:04 AM   #1
Caboclo
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Brass Length Tolerance

Regarding straight-wall pistol cases, I've read in several places that consistent case length is critical to getting a consistent taper. How consistent are we talking here? 0.001"? 0.010"? I'm willing to take the time to do it right, but don't want to waste time unnecessarily.
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Old November 30, 2009, 08:27 AM   #2
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Consistent case length would be nice but it's not going to happen unless you trim all of your cases back to the length of the shortest one. It doesn't matter that much on a straight case. Crimping is not as important as having sufficient case neck tension on the bullet. Neck tension does a far better job at holding the bullet in place than crimping the case. You should measure your bullet's dia. and then measure the expander plug inside your flare die. The expander plug needs to be at least 3 or 4 thous. in. smaller than the bullet diameter so that when you seat a bullet without crimping you can hold the round in your hand and push it on the edge of your bench HARD and have no movement of the bullet into the case. If your rounds pass this test the amount of crimp applied can be fairly light and you won't have setback or pull. By using a minimum amount of flaring and crimping your cases will last much longer than they will if you use a heavy crimp to prevent movement. Trying to stop bullet movement with a heavy crimp won't work and will cause other problems. Seating and crimping should be done in two seperate steps. Check out Lyman's M-step expander dies, they flare the case precisely and put less stress on the mouth. I have used them on .357 and .41/.44 Mag. cases that are twenty years old and have never had one split. Never had a bullet pull with heavy recoil/heavy bullet loads. This was how Elmer Keith constructed his heavy loads. He was a pretty clever old guy.
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Old November 30, 2009, 03:35 PM   #3
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My experience has been straight wall pistol cases don't stretch and over time they actually shrink. Unlike bottle neck rifle cases I don't even bother measuring case length and just shoot them until the case cracks or the case is lost.
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Old December 1, 2009, 01:33 PM   #4
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Consistency...

Caboclo--You said
Quote:
I've read in several places that consistent case length is critical to getting a consistent taper.
I think what you mean is a consistent crimp on the bullet, not consistent taper. If you're reloading for target shooting, and you're pretty good at it, a consistent crimp will help your accuracy.

If you're loading for just plinking, etc, then the case length in pistols, especially revolvers, is kind of unimportant.

For my target loads, in .357 Mag cases, loaded to .38 Spl levels, I trim the cases to 1.280-1.285". And that's probably fussier than I need to be. No deburring nor chamferring for straight-wall pistol cases, BTW--The bell-mouthing takes care of the chamferring and the crimping removes any bur that might exist.
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Old December 1, 2009, 02:12 PM   #5
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A taper crimp is less fussy about case length than a roll crimp. Also, the short, straight walled pistol cases hardly stretch compared to the rifle cases. In my experience the case mouths will crack from work hardening before they lengthen significantly. So I try to limit case mouth belling and crimping to the bare minimum.

Given all this, I never trim my pistol cases. I taper crimp only enough to take out the belling of the case mouth. About .001" less than the listed case mouth diameter in the case dimensional drawings. I run a few dummy rounds through the loading sequence (minus the primer and powder) to ensure the final dimensions are good for all of them. I've never found the taper crimp to work for some cases and not for others in a mixed batch. One setting works fine for all my cases.
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Old December 1, 2009, 04:25 PM   #6
Caboclo
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Cool, thanks for the info.
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Old December 1, 2009, 07:33 PM   #7
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Quote:
My experience has been straight wall pistol cases don't stretch and over time they actually shrink. Unlike bottle neck rifle cases I don't even bother measuring case length and just shoot them until the case cracks or the case is lost.
That would make sense to me. I only reload straight walled pistol rounds right now, so I can't speak about necked cases (but this thread is about straight walled anyways). And I'm not too picky about case length.

So in theory, casings expand and change dimension when fired (we know that), if you expand a straight walled case, the material has to come from somewhere. Yes brass has a certain amount of elasticity and most of the material comes from the wall thickness, but I could see where that expansion could shorten the over all case length a little (like .0001). Does that make sense? Thoughts? Opinions?
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Old December 1, 2009, 10:30 PM   #8
drail
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It's true, they do get shorter! Just make sure you remove the flaring and don't worry about it too much. Taper crimps are good.
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Old December 2, 2009, 10:54 PM   #9
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Schweet!!! thanks guys
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Old December 3, 2009, 12:39 AM   #10
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All that specific advice and no one asked what caliber you were loading. In .30 Carbine (Ruger Blackhawk) I get a lot of case expansion. The round spaces off the neck. The gun really jams if the case length is a bit too much. It seems I trim just about after every other useage. I've not noted the same case stretching with 9mm, .357 magnum, or .44 magnum.
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