What is the difference between a roll crimp and a taper crimp?

[johngalt]

As I'm reading these replies, I have a question. If roll crimps are for revolver rounds to prevent bullet movement, and taper crimps are for auto loads, why does Lee sell a taper crimp for 38 spl/357? Also-if I use a taper crimp on my revolver loads, am I wasting my time?

A taper crimp is normally used for light target loads using soft lead bullets without crimp grooves. Light target loads using fast powders don't need a roll crimp to prevent bullets from jumping the groove. A taper crimp also works the brass less, so it will last longer.

A common mistake is assuming that because a roll crimp is used to stop a bullet pull under recoil, a taper crimp in an auto prevents bullet setback. It does not, the taper crimp just undoes the case mouth belling done before seating the bullet. Too much taper crimp decreases neck tension and makes setback problems worse.

 

[mrfluffy1989]

Yep, the center pic is too much crimp. Caption for the pic, explaining the crimps, was not included in my post...

So what do I do if my bair seating die that also puts a crimp on the round puts too much of a crimp on the round? Mine come out like the center picture. I'm a total noob by the way.

Thank you.

 

[Mad_Charlie]

I wouldn't use a roll crimp on 9mm.

 

[Troystat]

Then there is the question of how much crimp with a taper crimp die, for my 1911 that is set up for bulleye shooting with a Kart barrel and using lead bullets the crimp I use measures around .465 which is pretty tight compared to to Federal 185 grain FMJ swc's which measured about .469 if I recall correctly. I would not try to crimp jacketed bullets as much as the lead ones. Of course it is best to test your loads in the gun you want to shoot them in and in most cases (bad pun intended) stick to as close to factory specs as possible especially for a starting point.

 

[rwsmith]

Don't roll crimp.....

Don't roll crimp 9mm, .40, 10mm or .45 ACP or any rimless semi auto because rather than headspacing on the rim of the cartridge like most revolvers, a semi auto cartridge headspaces on the mouth of the case which catches on the slim rim in the front of the chamber. If you roll crimp these, there is a chance than the cartridge will drop deeper into the chamber and cause misfires because the cartridge is away from the firing pin. It may not be too good for your chamber either.

A taper crimp will allow a semi auto cartridge to drop into the chamber and headspace properly on the front of the chamber.

 

[model3sw]

Just found this old thread, posting a "I LIKE IT" so it will be retrieved from the archives up to the top for awhile.