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Old August 2, 2011, 10:55 PM   #1
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Crimping Information! PLEASE HELP

I would like someone or many people to genuinly teach me everything about crimping and dies. Just explain everything such as sizes, dies, crimps, tapers, rolls, and etc. Just give me a long helpful guide to what these words mean. I already have a basic knowledge. But I must learn more. Please feel free to write a book in this thread to help explain the definitions and more.
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Old August 3, 2011, 12:12 AM   #2
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Hello, Usertag. My life is too busy to write a book...Why don't YOU buy a few good reloading books and read them at your leasure..You'll most likely retain the info better & have them on hand for future reference.
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Old August 3, 2011, 12:23 AM   #3
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Rather than many us typing our fingers off and still maybe not getting it all correct from memory, I would suggest the following: A copy of a book on reloading. The ABC’s of Reloading comes to mind, and/or a reloading manual, or two, there are several of them. Read them, cover to cover, not just the load tables, even the instructions that come with reloading dies are pretty informative. Not only will you have most of your questions answered you’ll have something to refer back to, written much better than any of us could do.
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Old August 3, 2011, 12:44 AM   #4
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The previous answers are dead-on. The forums are best suited for answering a specific question. Also, there is a good chance that anyone's attempt to answer general questions will be incomplete, and possibly dangerous.

Nevertheless, I'll give you a summary, with the understanding that a more complete treatment is available in reloading manuals and texts -
  • Size - If you mean "degree of crimp", this is like Goldilocks (not too hot, not too cold, just right.) Excessive crimp can bulge the case and cause chambering problems. Insufficient crimp can cause things like bullet pull (in revolvers) or setback (in rifles with tubular magazines), and also cause chambering problems in semi-auto pistols if the bell isn't removed.
  • Dies - There are combination seat/crimp dies and separate seat and crimp dies. It is generally easier to use separate dies, as the two actions "fight"' each other to some extent in a combination die.
  • Crimp - Forming the mouth of the case using a die.
  • Roll Crimp - A type of crimp which "rolls" the mouth of the case into a groove or cannelure in the bullet designed to receive it. Roll crimps applied to bullets without either of these usually damage the bullet and degrade accuracy. Usually used with revolver cartridges, especially magnums.
  • Taper Crimp - A type of crimp which removes the "bell" created by an expander die to make bullet seating easier. Taper crimps should not roll the case mouth. Usually used with semi-auto pistol cartridges.

And, for completeness, there are two flavors of Lee Factory Crimp Die which need to be separately researched and judged on their own merit.
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Old August 3, 2011, 01:28 AM   #5
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Look at the definitions at this site:

Read all that apply to get a better understanding.
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Old August 3, 2011, 05:32 AM   #6
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I know the answers sound harsh, but they are right.

It would be better to know which round you are talking about. Some need to be crimped, some do not. Some need a heavy crimp, some work best with a taper crimp, others with a rolled crimp.

As for how to set up a separate crimping die, best to read the instructions that came with that die.
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Old August 3, 2011, 09:45 AM   #7
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Crimping & Goldilocks have a great deal in common... right up there with kissing a lot of frogs until finding the one(s) that's juuuust riiiiight.


But because eating all that porridge can get so tedious (and you already met a lot of frogs in high school), realize that things are fairly simple:

There are really only two types of crimp:
(1) one that smoothly "rolls" the case mouth over and into the bullet; and
(2) one that "squeezes" the case mouth into the bullet in a taper (no rollover).
There are endless variations on these two themes, but that's about it in a nutshell.

Remember a couple of other things....


- Most rifle cartridges "need" no crimp. If you just have to have a crimp, make sure you have a bullet manufactured w/ a crimping groove already in it. Otherwise you'll just make matters worse.

- Rifle cartridges in tubular/lever action magazines probably do need to be crimped. Make sure you use bullets that don't have an appreciable point, and that do have that crimping groove mentioned above.

- If/when a crimp is used, rifles generally use roll crimps.


Pistol cartridges do need crimps when:

- You have a heavy bullet in a heavy-recoiling revolver. There the bullets tend to back out of the case under that recoil, and can actually interefere w/ cylinder rotation if not secured. Whether a crimp in actually required can be known in just a few shots. Revolvers generally take roll crimps and the bullets need to have a crimping groove.

- You have an automatic in which (a) the case mouth has been "belled" to seat the bullet and therefore requires straightening out to finish the reloading; and/or the case mouth is used to headspace the case in the chamber and whose diameter therefore needs to be precisely reshaped to feed correctly. In either case, automatics take tapered crimps.

Roll crimps can be perfomed simultaneously while seating if the die is properly adjusted for proper no-crimp seating first; then the seater is backed out and the die screwed in for proper [not overly-gorilla'd] crimping; then the seater is screwed back in to contact the bullet while fully up in the die. The die is then set to both seat and crimp w/ one motion. Some people still prefer to crimp as the last step. (Only the frog process can teach you that.)

I find that taper crimps on autos is best done as the last separate step.
`Just my opinion, but I got tired of frogs in my old age.

post script: Fewer frogs are required if one reads the die instructions.

Last edited by mehavey; August 3, 2011 at 10:59 AM.
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crimp , die , roll , taper

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