Taper crimping

[chaneyd]

Just started reloading in April with no problems so far. Have a Dillon 550B and load 9mm, 10, 40, 45 and 44mag. My question is about the roll crimp vs taper crimp. I think I'm taper crimping everything.

I taper enough to get rid of the bell and allow the bullet to drop in my Dillon case gage. I also check it by dropping it into my Glock barrel. No problems so far. When I first started, I couldn't get the bullets to drop completely into the gage or barrel and determined it was not enough crimp.

Am I correct in doing it this way?

Thanks in advance.

[Unclenick]

Welcome to the fourm.

The .44 Mag or any other revolver round except extremely light revolver target loads will need the roll crimp. This is because the revolver's recoil drives the cylinder back against the rims of the unfired rounds. Those rounds have no magazine wall or other object to hold the noses in place, so that inertial shove can work their bullets out of the cases with recoil, until they stick out beyond the cylinder face, thus jamming the cylinder from rotating. Think of the revolver as a weak inertial bullet puller for the unfired rounds. The roll crimp is needed to prevent this by hanging onto the bullet like a claw.

In self-loaders the main worry is the bullets being pushed deeper into the case when the magazine recoils into them or when they are shoved into contact with the loading ramp by the slide. Pushed-in bullets raise pressure dramatically, so use of the taper crimp to form a wedge against that push-back is all you need. It needs to slightly indent a lead bullet or go into a crimp groove to do this, so don't make it too weak with lead bullets. Jacketed bullets often don't need a crimp for self-loader use because the bullets require a lot of seating pressure, where lead will often slide deeper under thumb pressure alone if the crimp doesn't dig into by, say, 1/3 of the brass thickness or so.

[chaneyd]

Thanks for the info. What is exactly a roll crimp compared to a taper crimp?

[D. Manley]

Thanks for the info. What is exactly a roll crimp compared to a taper crimp?

Here's a graphic over-simplified of the difference:

[chaneyd]

What gets the taper crimp?

[bobotech]

Semi-autos for the most part.

Cartridges that don't have rims such as the 45acp/9mm/40s&w/308acp/etc. Cartridges that do have rims are like the 44mag/357mag/revolver cartridges.

If its a bottom feeder, it more than likely will take a taper crimp, if its a wheel gun with a rimmed cartridge, it will take a roll crimp.

You can roll crimp 45acp if you are shooting it with moon clips in some revolvers but i'm not sure if that is useful or not, but you would NOT want to shoot roll crimped 45acp out of a semi-auto pistol.

The reason for that is because unless you are using moon clips in a revolver, the taper crimped round headspaces off the case mouth. You roll crimp it, it can cause problems with headspacing.

[Unclenick]

Actually, if you look through old issues of the Rifleman from the 60's and in that era when they still used to publish the loads used by top target shooting champions, you will find almost all of them shot the .45 ACP with H&G 68's with roll crimps dug in below the leading edge of the bullet bearing surface. Many still claim that's most accurate loading method because of better shot start pressure uniformity, but you do need the bullet seated out far enough to headspace on the throat before that crimp touches down. Otherwise it will try to open into into the throat, creating high pressure. Either that or you headspace off the extractor hook so it stops the round from going too far forward, though that usually is not good for lead bullet accuracy.

I've used the taper crimp in semi-autos for so long without accuracy problems that I've never experimented with that old-school approach. I don't want the case life reduction, for one.