How much does crimp effect power factor?

[Superpipe9]

How much does the crimp effect power factor? I recently loosened my crimp very slightly and found that my PF went down from 134 to 131. I can't think of anything else that changed.

135gr bayou bullet

3.4gr titegroup

1.110 OAL

[cnote]

nope, another variable, unless you were cutting into the coating, which is bad in the first place

[Hi-Power Jack]

You may not have fired enough rounds over your chrono - you'll

get variation in your PF.

I usually fire 20 over the chrono, and realize that if I fired another

20 over the chrono, my PF would change.

The larger the sample, the more positive you are about what

your PF actually is.

[Vlad]

It depends. I used to think none, but recent experiments on my part plus advice from the statisticians at Western has convinced me that "it depends". Chrono some more, vary ONLY the crimp and chrono some more. I think different powders and different bullets will react differently to changes in crimp.

[bowenbuilt]

The roll crimp on a revolver round can have a dramatic effect on consistency. Since an auto pistol round is not "crimped" it has NO effect on the round unless you are using the auto round in a revolver and roll crimping. If you over crimp an auto round with a taper crimp die which is really swaging not crimping, it will cause all kinds of problems. If you can see a difference in an auto round chances are you are over crimping/swaging which also causes tumbling, smoking and leading. So, if you are speaking of an auto round, used in an auto pistol using a taper crimp type die there is no difference in velocity that could be related to crimping unless you are doing it wrong. The only thing holding an auto pistol round in place is the neck tension between the bullet and the case. Taper crimping has nothing to do with this aspect unless you over do it. If you over do it, it can decrease neck tension which will effect velocity and bullet stability.

Edited June 27, 2015 by bowenbuilt

[peterthefish]

How much does the crimp effect power factor? I recently loosened my crimp very slightly and found that my PF went down from 134 to 131. I can't think of anything else that changed.

135gr bayou bullet

3.4gr titegroup

1.110 OAL

Can I be the first to say, temperature? What was the temp on each day at the time you shot them (assuming ammo had time to come to ambient temp). Also take into account if it was in sun, shade, etc...

[cnote]

The roll crimp on a revolver round can have a dramatic effect on consistency. Since an auto pistol round is not "crimped" it has NO effect on the round unless you are using the auto round in a revolver and roll crimping. If you over crimp an auto round with a taper crimp die which is really swaging not crimping, it will cause all kinds of problems. If you can see a difference in an auto round chances are you are over crimping/swaging which also causes tumbling, smoking and leading. So, if you are speaking of an auto round, used in an auto pistol using a taper crimp type die there is no difference in velocity that could be related to crimping unless you are doing it wrong. The only thing holding an auto pistol round in place is the neck tension between the bullet and the case. Taper crimping has nothing to do with this aspect unless you over do it. If you over do it, it can decrease neck tension which will effect velocity and bullet stability.

A very detailed and eloquent way of repeating what I said, and Bowen knows his stuff!!