Taper Crimp vs Factory Crimp

[Bret]

I use the taper crimp for pistol/straight walled rounds & factory crimp for rifle/necked down rounds.

This is my thought too, so I'm not understanding the concept of using a taper crimp on a bottle necked rifle cartridge. For background, I'll start by saying that my belief is the purpose of taper crimping a straight walled pistol cartridge is to remove the remaining flare from the belling step. The purpose is not to help hold the bullet like a roll crimp or bottle necked cartridge factory crimp does. So, what does taper crimping a bottle necked rifle cartridge actually do? There is no belling of the case mouth, so there is no mouth flare to remove.

[markm]

This is my thought too, so I'm not understanding the concept of using a taper crimp on a bottle necked rifle cartridge. For background, I'll start by saying that my belief is the purpose of taper crimping a straight walled pistol cartridge is to remove the remaining flare from the belling step. The purpose is not to help hold the bullet like a roll crimp or bottle necked cartridge factory crimp does. So, what does taper crimping a bottle necked rifle cartridge actually do? There is no belling of the case mouth, so there is no mouth flare to remove.

You're correct on the pistol taper crimp. With the rifle, there's a couple of ways to look at it. First one is if you have a cannalure on the jacket, you can taper the neck into the cannalure to mimic what you'd find on military m193 or whatever.

For the purposes of this test, there were no cannalure bullets. So the crimp was to uniform the neck tension in lieu of annealing the cases. So the crimp is set fairly lightly since there's no cannalure. And the results may or may not support the crimp helping accuracy. Really a much larger test would probably be necessary to say for sure.

[Bimmer]

I always apply a light crimp to improve consistency, and have had great results.

Consistency of what?

I'm not trying to pick a fight, just trying to understand all this...

In the slam bam world of a push feed semiautomatic rifle, how much neck tension can reliably hold a bullet without a crimp?

Somebody correct me, but AFAIK it's all about neck tension, and crimping is just to remove any bell...

I'll start by saying that my belief is the purpose of taper crimping a straight walled pistol cartridge is to remove the remaining flare from the belling step.... There is no belling of the case mouth, so there is no mouth flare to remove.

This was my understanding, too...

So the crimp was to uniform the neck tension in lieu of annealing the cases... Really a much larger test would probably be necessary to say for sure.

I appreciate you posting this kind of stuff, with empirical data to back it up. (I'm such a geek.)

Given that slight variances in case length would impact the tightness of the crimp, it seems to me that you're simply adding another variable, rather than directly offsetting any variance in neck tension.

I hesitate to be the guy who asks for yet more testing, but it would've been nice to see some chrono data on these rounds... If crimping improved ES/SD, then that would make me think "more consistent tension." If not (or the reverse), then I remain skeptical.

[BobinNC]

Given that slight variances in case length would impact the tightness of the crimp, it seems to me that you're simply adding another variable, rather than directly offsetting any variance in neck tension.

Not questioning your skepticism, nor asking to buy a pig in a poke, but the Lee FCD doesn't care about slight variances in case length. Case length does not impact the tightness of the crimp at all with the FCD.

[Bimmer]

... the Lee FCD doesn't care about slight variances in case length. Case length does not impact the tightness of the crimp at all with the FCD.

10-4. I was thinking of the taper crimp...

[grizzman]

Consistency of what?

I'm not trying to pick a fight, just trying to understand .

Consistency of neck tension.

[markm]

Yeah.. there might be some length variances due to the Giraud trimmer indexing off the shoulder, not the head, but I'm convinced it's negligible... even for the taper. I did chrono testing years back on all 3 and there were no noteworthy variations in velocity. I remember thinking the test was silly and for velocity, the crimp made no significant impact.