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Old December 14, 2001, 03:17 AM   #1
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Join Date: June 18, 2000
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Confused about taper crimping

I've reloaded a lot of revolver rounds but am just now starting to reload semiauto rounds. I've done a search concerning crimping them and haven't really figured it out yet.

I think I understand the differences between the roll crimp and taper crimp.

I purchased some new Hornady Titatanium Nitride dies to load 45ACP. Previously I have worked with Lee Dies for revolvers. The instructions with the Hornady dies say nothing about taper crimping or roll crimping, just "crimping". Can someone tell me what kind of crimping they perform? I've read other posts about roll crimping vs taper crimping and have been lead to even more confusion. If autoloaders are not meant to be roll crimped, then why would die sets for autoloaders have the roll crimp function?
If die sets for autoloaders do not normally taper crimp and a taper crimp is really necessary, why don't the manufacturers include a taper crimp die with the set?

The cast lead bullets I have do not have a crimp groove. Loading for revolvers, I could see the effects of a roll crimp very well. I've experimented with these new dies and no matter how much I adjust the die, there is no "roll" noticed. There is still a nice sharp edge left at the case mouth. Is this because there is no crimp groove for the brass to "roll" into or because the die doesn't roll crimp?

Other posts I've read have a lot of differing opinion concering crimps and whether or not they are necessary. Some have said the taper crimp simply smooths out the bell in the case created by the expander die.

Here is what I've done so far. I followed the instructions provided with the Hornady dies to make powderless, primerless dummy rounds to see what I'd get. I got the right seating depth set up and adjusted the crimp (whatever kind it is) just a little to where the bell in the case is gone. I then took a barrel and put the rounds in the chamber to see how they would fit while comparing them to new factory loaded ammunition and it's fit and heatspacing. I've ended up with something that appears it will feed and extract smoothly. I cannot push the bullets deeper into the cases with fingers; the bullets appear to be very tightly held in the case neck (can actually see an outline in the brass where the bullet is seated to). I'm failing to see how a crimp in this cartidges is even necessary, other than to get rid of the flare from expanding.

Any help would be appreciated. I'd like to make sure I'm not doing anything unsafe before putting powder in one of these and making it go bang.
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Old December 14, 2001, 04:18 AM   #2
Bill Adair
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Join Date: April 18, 2000
Location: Seattle/Tacoma, WA USA
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All auto die sets utilize taper crimping, while revolver die sets use roll crimping. However, taper crimp dies are available for most revolver cartridges, and I use them for many bullets that do not have a crimp groove.

If you can find a book or gun store that stocks the Lyman Pistol and Revolver Reloading Handbook, Second Edition, there are nice illustrations of the crimp types on page 60 and 63. Probably older editions have the same illustration.

Before I bought this book, I used to measure the neck diameter of a factory round just behind the edge of the case mouth (1/32"?), and taper crimp to the same diameter. That also worked, but the book shows it superbly.

Revolver bullets with crimp grooves are much easier to judge, as I simply roll the case mouth in so that it is just behind the front of the groove (with no gap), and is rolled in just far enough to touch the bottom of the groove. The manual shows that very well.

It's very easy to get over aggressive with crimping, and it usually results in bulged cases that will not feed properly. The idea is to get the case mouth snug on the bullet, but not deform the bullet or case.

Don't feel bad about your confusion, as only the better manuals cover this in a clear and concise manor.

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Old December 14, 2001, 04:54 AM   #3
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Join Date: August 29, 1999
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You are doing it right! I would second Bill's advice on that little Lyman book. Although it isn't very big, there are some good tidbits in there. Also, their Cast Bullet Manual is a good one as well.

As for amount of crimp, look at the specifications for the particular semiauto cartridge you are using. In other words, look at the spec. for the case mouth diameter in the respective cartridge drawing. That is the maximum diameter allowed. I usually crimp to that or around .0005 under that diameter for light loads. For heavy/hot loads with slow burning powder I go up to .002 under the maximum allowed case mouth diameter. That is measuring at the extreme edge of the case mouth. Do those qualify as light crimps or heavy crimps? Who knows. Guess it depends on the reloader!

You will see a lot of people saying "use a light crimp" or "use a heavy crimp". Unfortunately, they never quantify their "light crimp" or "heavy crimp" in terms of how much under max case mouth diameter that is.
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