Crimping De-Mystified.

By Mike “Duke” Venturino

Over the years I’ve done reloading seminars for cowboy action shooters. There seemed to be a universal lack of understanding when it came to crimping. If there’s one thing I’m sure of regarding handloads for revolvers or autos, is there must be some sort of crimp applied.

There are two basic ways to accomplish this. With cartridges that don’t headspace on the case mouth — revolvers or autos — a roll crimp is standard procedure. With semi-auto rounds headspacing on the case mouth, a taper crimp is normal. A taper crimp can be applied to revolver cartridges, although it might not be sufficient to keep a bullet locked in place with heavy magnum loads.

Actually, there’s a third way of crimping bullets, but to the best of my knowledge it can only be done at the factory on the assembly line. Those are called stab-crimps and are actually a spot where a hardened pin or rod has pressed against the cartridge case at different points around its circumference. This pushes a bit of the case into the side of the bullet. Stab-crimps are mostly seen on military ammunition.

Different types of crimps Duke applies to his World War II handgun loads.
From left: 7.62×25 Tokarov, roll crimped; 7.65 French Long, taper crimped;
8mm Nambu, roll crimped; 9mm Parabellum, taper crimped; .380 British Revolver,
roll crimped; .45 ACP, taper crimped and .455 Webley, roll crimped.

The Truth

The purpose of any crimp is simply to lock the bullet solidly in the cartridge case. The results and possible dangers of not crimping are several. With revolvers, if a bullet moves forward in the cartridge case it can end up protruding from the chamber — which will tie up the cylinder. That’s the best case scenario. Worst case scenario is the bullet moves forward, in effect increasing case capacity. If the propellant used is one of the hard-to-ignite types then the load might misfire — or even worse — squib. A squib is when the powder partially ignites, then it’s possible for a bullet to only go partway up the barrel, creating a block. Firing another round then could lead to disaster!

With autoloading pistols a loose bullet moving in the other direction can also be dangerous. There must be a taper crimp on the bullet to keep it from getting pressed into the case as it travels from the magazine, up the feed ramp and into the chamber. When this happens, case capacity is diminished, pressures rise and the result can be a ruptured case, releasing high pressure gas into the pistol. That’s a recipe for disaster.

Almost all bullets designed for revolvers have a crimping groove or cannulure so case mouths can be roll-crimped into them. Yet, almost all bullets designed for autoloading pistols are completely smooth sided. Taper crimps press case walls against the smooth bullet’s side, and taper crimp dies are minimally adjustable to help gauge that pressure. Usually the proper procedure is to set the die so the shell holder comes up against its bottom. Then the full amount of taper crimp is applied.

Here’s a factory loaded Romanian 7.62×25 Tokarov and a US .30 Carbine. Note the stab-crimp on
the Romanian round. The .30 Carbine must be taper crimped because it headspaces on the case mouth.

Don’t Crumple

Roll crimps can be adjusted from barely turning the case mouth toward the crimping groove — or cannulure — to rolling it in so far the case crumples. How much crimp is enough? At those cowboy action seminars I always told the cowboys, “Run your index finger from the bullet of your loaded round down and across the case mouth. If your finger nail hangs up on the case mouth — you don’t have enough crimp!”

Sometimes the seating/crimping die in a standard die set is substandard. It will roll crimp the case mouth properly on one side — but hardly touch it on the other. Some reloading tool companies have come out with specialized crimping dies to address things like this. Lee has their Factory Crimp dies and Redding has their Profile Crimp dies. I’ve used both with total satisfaction, and to be honest, the roll crimp dies in about 98 percent of the die sets I’ve used for the past 47 years have been fine too.

To paraphrase Mr. Spock, “Crimp heavily and crimp tightly — so you will live long and prosper.”

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