Bob Loblaw

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Feb 28, 2008
Buda, Tx
I haven't been reloading long, but somehow I missed the discussion on crimping. I've been firing my .40 reloads for some time using unique with no problems. I recently bought a new powder (HS6), as my old supply is running low, and while doing load research I noticed the discussions on crimping and keyholes... let me cut to the chase, am I going to kill my gun? I don't want to do that, I'm not looking for super accurate loads, I never shoot further than 15 yards (mainly cause I suck), but I like reusing my brass. So what should I do?


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Apr 28, 2008
The crimp is required not only for accuracy but for safety especially if your using a semi-auto pistol.

The reason to crimp a semi-auto pistol round is to insure there is no chance of bullet setback when the pistol racks a fresh round into the chamber. If there's little or no mouth tension on the bullet, a projectile could be pushed back into the case and raise pressures exponentially. This is a very unsafe condition and can cause a kaboom!

To test your crimp you can press the bullet point against a wood block and apply pressure to the cartridge to see if you can press the bullet back into the case.

Another reason to crimp is to allow sufficient pressure to build up in the case before the bullet begins to move. This can sometimes make a big difference in the accuracy.

One of the best crimp dies I have found is the Lee Factory crimp that not only does a great job crimping but also irons out the bulges that you sometimes get when seating. It allows me to skip case gauging each cartridge because the Lee crimps and sizes the entire length of the cartridge assuring me each cartridge will chamber without a problem.

Hope this helps,



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Jul 10, 2008
Forney, TX
I taper crimp my 45ACP with Lee factory crimp die that came with Lee deluxe pistol set. .469-.471 diameter after crimp.

I roll crimp my 41mag with the seating die that came with my Lee Pro 1000 kit.

I roll crimp some rifle, but generally do not. If it is semi-auto or tube-fed, then I would roll crimp. My dad's RCBS die set came with bullet seater with roll crimp. You just bump the press at end of stroke to crimp. My Lee deluxe rifle dies did not come with crimp, so my 7mm mag doesn't get a crimp.

Some folks say always crimp. I shot a lot of the 41magnum with no crimp. The 45ACP loads better after I crimp. I bought a Dillon case gage to check so I don't have to use my gun.


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Mar 4, 2008
With straight walled pistol cartridges, the primary tension which prevents bullet setback in case during feeding is the tension which results from sizing the case during reloading. The primary purpose of taper crimping a straight walled pistol cartridge is to remove the belling/flaring applied during reloading to facilitate bullet seating. In fact, excessive taper crimping after bullet seating can actually serve to loosen the case hold on bullet due to different spring back characteristics of lead bullet and brass case.


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May 4, 2008
That is the way I understand it, I crimp my .40 and .45 just enough to "unflare" the mouth.


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Aug 11, 2008
Ontario, Canada
With RCBS 3 die carbide sets I was getting a bit of case bulge that would cause the round to partially chamber in autos .45 ACP, .40 S&W, 10mm (OK in 9mm). Also getting tight fits in revolvers .38 SPC and up. I ended up getting Lee factory crimp dies for all my handgun calibers as well as one for 30-06 (needs a heavy crimp when you're port loading a lever action tip to base). I still use the RCBS dies but seat without crimp then run them through the lee die. It resizes the seated round and crimps on the down stroke then resizes again on the upstroke which leaves you with finished round that drops into the chamber.



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