crimping and accuracy..

[sixxgunnernick]

Hey guys and girls..does crimping bullets have any effect on accuracy?

[1911rocks]

Good question!! It's a two component matter. First, the crimp does affect accuracy from the standpoint of consistency. If each bullet is gripped by the case with the same force, and the amount of propellant is equal, and the case volume is equal, and the bullet weight is equal, and the COAL is equal then the bullet will be leaving the barrel very similarly shot after shot. This does not account for variation in powder. This alone can fill volumes.
The second component here is case length. The crimp is also based on case length. This is particularly true in rounds like .223, .308, the bottle necked cases. Years ago Handgun Silhouette shooters realized the need to trim to length cases such as 44 mag, 41 mag, etc. for this crimp consistency issue. Many handgunners never bother with case length because they don't see an major need. True the low pressure rounds like 44spec, 38spec, 45LC, 45acp don't see much stretch. However, 9mm, 40sw, 10mm, 38 Super and all the magnums do indeed stretch. Especially the 38 Super. This was a big reason for the early reliability problems with 38 Super loaded hot to make Major in IPSC and the older headspaced barrels (another story). I hope this helped and didn't bore you too badly.

[sixxgunnernick]

Didn't bore me at all..thanks for the reply!! I was shooting the same everything as in powder..rounds..weight ect. and I was shooting the bullseye out. But then I loosened up my crimp a tad and shot around the bullseye. If it works don't change it I know. I was shooting low after I loosened my crimp. It seems like crimping does affect accuracy but thought someone knows for sure. The rounds are .45 acp 230 grains by the way. So I'll just snug up the crimp a tad and see if it helps on my next batch.

[WESHOOT2]

It can, it does, I test.

I use (mostly) LEE Carbide Factory Crimp dies for finishing autoloader cartridges, and Redding Profile Crimp dies for revolver cartridges.

I vary crimp, take ten steps, shoot, return those ten steps, and readjust crimp and retest.

I have found it matters MORE for revolver cartridges, but if adjusted improperly, can have negative affect on 'auto' cartridges.

Autos: A wee bit into the bullet, fully removing ALL flare.

Wheels: Medium-firm is my most-used adjustment, because most of my loads are NOT MAX. Easy tip: Visit your friendly local gunshop, open some boxes of high-end ammo, and visually inspect THOSE crimps.

[gearheadpyro]

I use the Lee factory crimp on SOME of my rifle ammo, mostly my hunting stuff. My Hornady SST's shoot much better with a medium crimp on them.

That being said, when I was using winchester cases with matchkings they did not like the crimp as much. I switched over to lapua brass and haven't yet had enough time to thoroughly test the results.

[Shoney]

Yes, crimping does make a difference, as has been noted above. In my experiences, contrary to 1911rocks statement, all the semi-auto pistol cases grow minimally shorter with each sizing, and never need trimming.

If you are roll crimping, pistol case length is important for consistent crimp. Some old 45ACP target shooters discovered better accuracy if they roll crimped their lead bullets. As with all short auto-pistol cases, the roll crimp would not headspace on the front of the chamber, but would be held against the slide face by the extractor, and give excellent results.

With taper crimp on auto-pistol cases, case length is less important, and consistent OAL is more important. With repeated sizings, the shorter cases will no longer headspace on the front of the chamber, but do well while heaspacing off the slide.

[sixxgunnernick]

I snugged up fifty rounds and went to the range last night..and it seems to help.