crimping

[dwtt]

I am reloading 9mm and haven't crimped the reloads before. Now I want to see if crimping will give more consistent muzzle velocity. So, does anyone use a taper crimp on their 9mm ammo and how much crimp do you give the case mouth? I'm reloading 124 gr FMJ RN bullets, with 4.2 gr Winchester 231, and a 1.125" OAL.
thanks.

[the86d]

I just give enough crimp to reverse/combat the belling done to insert the bullet, but this is pretty minimal on the 9mm I have reloaded. I am not sure that any real belling even occurs on a XL 650 for 9mm, as I have never taken the calipers to brass after a powder drop. I think I set the die to 1/16-1/10 turn after brass contact, if I recall correctly.

[ireload]

I taper crimp my 9mm. I crimp just past the minimum setting. More like between minimum to medium. But I'm also anal with my trim lenght so I can come close to uniform crimp as possible. It'll give you more consistent MV if you factor in same brand brass, trim length, same powder weight etc.

[the86d]

I didn't know we should trim straight walled brass. Time to read more...

<Goes off to O.G. ReadMore...>

Read more, and back: "I have never trimmed a single piece of pistol brass in more than 50 years of reloading."

http://smith-wessonforum.com/reloading/216685-trimming-9mm.html#post136192113

Then: "Me either in 41 years of reloading Another voice joins the choir"

I am not so worried about trimming 9mm brass anymore.

My 5.56 brass likes a bit of trimming.

[Bill Steele]

In general, you want to only take the belling out of the case with your taper crimp die. Some people (me included), crimp their LSWC .45ACP down below the "just take the belling out" level for feeding reasons.

Taper crimps lessen neck tension, rather than increase it. If you are taper crimping enough to actually increase the hold on the bullet, you are damaging the bullet and hence creating other potential problems.

Brass has more spring in it than lead, so as you crimp down the lead deforms and doesn't snap back, the brass deforms but snaps back a little more than the lead below it, hence neck tension lessened. Make sense?

The crimp to improve burn consistency argument applies more to roll crimped cartridges (bullets have a cannelure and case has a rim on it, on which the cartridge headspaces) and generally is more related to magnum handgun and rifle speed burn rate powders.

[dbbspider]

In general, you want to only take the belling out of the case with your taper crimp die. Some people (me included), crimp their LSWC .45ACP down below the "just take the belling out" level for feeding reasons.

Taper crimps lessen neck tension, rather than increase it. If you are taper crimping enough to actually increase the hold on the bullet, you are damaging the bullet and hence creating other potential problems.

Brass has more spring in it than lead, so as you crimp down the lead deforms and doesn't snap back, the brass deforms but snaps back a little more than the lead below it, hence neck tension lessened. Make sense?

The crimp to improve burn consistency argument applies more to roll crimped cartridges (bullets have a cannelure and case has a rim on it, on which the cartridge headspaces) and generally is more related to magnum handgun and rifle speed burn rate powders.

+1

[huckberry668]

straight wall autoloader rounds like 9x19, 45acp, 40sw etc headspaces on the case mouth. You should only taper crimp them. Roll crimped mouth may get small enough to get pinched by the leade (start of the rifling) and create extreme pressure. I'm not even sure they make roll crimp dies for these calibers.

I did some test years ago with amount of crimp. It burns cleaner with more crimp but you kill accuracy. rifle or pistol rounds. Nowadays I crimp to remove bell only like others have said here.

Autoloader rounds are hard to put a uniformed crimp on if you reload mixed head stamps. The case lengths can vary up to .020". Since crimp dies work off of the full case length you'll never get a uniformed crimp if you don't trim.

The results are even more pronounced in rimmed revolver rounds. I shot customed revolvers in my PPC & Bianchi Cup competition days. untrimmed brass yielded much less accuracy with the same load compared to trimmed ones.

Should you trim? No, if you're not after extreme accuracy. You should if you want to win matches in my opinion and experience.

here is an article from someone who did an accuracy test with 9x19.

http://www.leverguns.com/articles/taylor/9mm_reloading.htm