An Interesting Crimping Discovery...

RVTECH · Mar 31, 2021

A few years ago I acquired a .357 mag collet crimp die and of course love it due to no longer having to deal with the inconsistencies of roll crimping with untrimmed brass but I still load .38 Special and would still have to roll crimp those.

Well, while messing around and thinking about it I stumbled on a great idea - take a .9mm (non-carbide) sizer die, remove the bullet seating stem, and use it to create a taper crimp !

Well guess what ? I tried it and it works perfectly! I adjusted it for firm, but not heavy pressure and the tapering effect of the sizer die gives it a smooth and obvious taper into the bullet.

This might only work with .38/.357 loads due to the similarity of case diameter with 9mm but it might help some out - providing they already have a set of 9mm dies, or a box of old dies & parts - like I do.

Member 34319 · Mar 31, 2021

I've used taper crimps, via an RCBS taper crimp die set, over roll crimps on bullets that do not have a roll crimp grove for quite some time. You'll be happy to grab a taper crimp die set if you can find one.

po18guy · Mar 31, 2021

Why not? Probably best to do this by 'feel' rather than setting, as brass thickness and case length will somewhat alter the result. With freshly trimmed cases of the same brand, I think a setting would work. Other variables are bullet diameter and construction (cast, jacketed, plated, powder-coated etc.). But, these are fine points.

RVTECH · Mar 31, 2021

Probably best to do this by 'feel' rather than setting, as brass thickness and case length will somewhat alter the result.

Actually this is proving not to be an issue and with a 'setting' all the crimps have essentially the same 'feel' on the press.

I believe the case thickness and minimal differences in length are inconsequential.

This is working well as a 'free' alternative to roll crimping which is problematic with untrimmed cases - which is why I like the collet crimp die as I do NOT trim pistol cases.

Darren Summers · Mar 31, 2021

I do use taper crimp dies but this is interesting. It's never too late to make new discoveries.

DizzyJ · Mar 31, 2021

Interesting indeed! I think that would be the cats meow for Bullets without a cannelure. Hopefully the taper crimp will hold the bullets solidly enough as to keep them from pulling out of the case with the heavier recoiling 357 loads.

RVTECH · Mar 31, 2021

Interesting indeed! I think that would be the cats meow for Bullets without a cannelure. Hopefully the taper crimp will hold the bullets solidly enough as to keep them from pulling out of the case with the heavier recoiling 357 loads.

It's working well with bullets with a cannelure as well.

I think they are as tight as a collet crimp or a prescribed taper crimp die.

I have pushed on one as hard as I could against the bench and no movement!

po18guy · Mar 31, 2021

I was speaking only in the technical. If it works, it works.

Pepe-lepew · Mar 31, 2021

DizzyJ said:
Interesting indeed! I think that would be the cats meow for Bullets without a cannelure. Hopefully the taper crimp will hold the bullets solidly enough as to keep them from pulling out of the case with the heavier recoiling 357 loads.

Taper crimping is to remove the bell in the case for bullet seating. It does not hold the bullet unless over crimping so much the bullet is deformed.

Xaevian · Mar 31, 2021

Now that's some stone cold crimpin' rollin' in those 38's!

Certaindeaf · Mar 31, 2021

I call that/those "post sizing" and not crimping proper. And the disparate "springback" of the two metals results in a lesser grip than were it not used at all.