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Old August 6, 2002, 03:45 PM   #1
bcgunner
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What is "crimp"?

What is "crimp" and where can I find info on the amount of crimp to use for the different calibers? I've never seen reloading data that mentions how much crimp to use.

TIA.
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Old August 6, 2002, 04:27 PM   #2
Steve Smith
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Where is this "crimp" and where can I get some?

Crimp is kind of a subjective thing, and topic dependent, too. crimp MAINLY deals with pistol cartridges.

Crimp to a small degree is just the removal of the flare that you put in a case to get the bullet started. To a further degree, crimp is an in-turned ring that actually "digs" into the bullet material or engages a sunken ring (cannelure) in the bullet.

In your load book (you do have one or two, right?) you'll see measurements for each cartridge. Do you see the diameter of the case mouth (the part the bullet goes into?) That measurement is the maximum size that case can be at that point. I'll use .45 acp for an example. On the .45 acp drawing, you'll see that the measrement is .473" That means that the case must be .473" OR LESS at that point in order for that part of the cartridge to function properly. Most semi-auto cartridges "headspace" on the case mouth (basically meaning where the length measurement starts from) Therefore, having a flat edge at the case mouth is important to getting the case to stop in the chamber at the same place every time. You don't really "crimp" a semi-auto case, you just remove the flare that you put in earlier, and leave the end of the case straight alongside the bullet. Semi-auto cartridges mainly rely on "case neck tension" to hold the bullet in place. With a revolver, the case headspaces on the rim, so the length and the flat edge of the mouth isn't so important. With some heavy-kicking rounds, the inertia of the bullets can make them "back out" of unfired cases, changing the dimensions of the cartridge. Some crimp at the mouth can help hold the bullet in place better. When you're doing this, you have to experiment a lot. A lot of crimp can be detrimental to case neck tension (provided by the sizing die) and actually loosen the hold that the case has on the bullet. Too little, and you get no added value to just case neck tension. Experimentation is necessary to see if any is needed, and if then, how much.

Remember, if you move the brass more than you have to, you're wearing it out faster than you need to.



BTW I am fighting a little battle in Gen Discussion, so I'm sorry if I'm being short. Lemme know if you have any other questions.
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Last edited by Steve Smith; August 6, 2002 at 04:49 PM.
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Old August 7, 2002, 09:01 AM   #3
Bacchus
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You also have to be careful about excessive crimping, too because it will raise case pressure.

Most recommend the minimum crimp, both to reduce pressure and to keep from over-working the brass like SS mentioned.
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Old August 7, 2002, 11:32 AM   #4
bcgunner
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Thanks guys for the responses.

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