Ever kind of ammunition has it's own technical needs. How each is put together varies by caliber, weapon, and intended use. A conscientious hand loader studies these variations and uses them to build safe, efficient, and high quality ammunition.
One of those variations is 'Crimp', or whether or not the brass case is clamped into the bullet by some means.
There are several types of crimp, each serving a different purpose on a different cartridge.
An old fashioned roll crimp, where the case mouth is literally 'rolled' into the bullet, is usually found on ammunition with straight walled cases. A roll crimp requires either a soft lead bullet for the case to impress, or more often a 'cannelure' on the bullet for the casing to be rolled into. Roll crimps see use in heavy recoiling revolver ammunition, and straight walled big bore cartridges like the 45/70. The heavy roll crimp serves several purposes, like most crimps: It keeps the bullet from walking out of the case in the magazine under recoil, it keeps the bullet from being rammed deeper into the case in the same situation, and it offers an initial resistance to bullet movement as the primer lights off the powder charge, giving higher velocities and lower velocity variations.
On a pistol round that headspaces on the case mouth (.45acp, 9x19mm, etc), a 'Taper' crimp is often used. This style crimp has the loaded round forced into a tapered die that presses the case mouth into the bullet evenly without rolling it over. It serves all the purposes of the roll crimp, while providing the very even and correctly sized case mouth that an autoloader requires. Taper crimping straight walled ammunition meant for autoloaders insures better feeding and more accurate headspacing.
Finally, and the discussion point for this article, we have a special kind of crimp offered by a line of LEE Precision dies. This type of crimp uses a collet die, and presses the case mouth straight into, or against, the side of the bullet. It can be used on bullets with or without a cannelure, as the case mouth is not actually rolled in.... but pressed against... the bullet.
The 'Factory Crimp Die' duplicates the crimp most often found on commercial factory high power rifle ammunition, thus it's name. Using this style crimp on bottle neck high power rifle cartridges offers the same advantages other crimps do, but is not a requirement when loading ammo such as .223 or 30-06. Cartridges such as that will perform just fine without a crimp.... and therein lies the question: Is it worth the time to do that extra step of running every freshly loaded case into the LEE Factory Crimp die?
Carteach's opinion.... for every reason that I crimp so many other cartridges I load, I'll do the same here. While the .223 does not require the crimp, for the purposes I use this cartridge it benefits enough from a run into the FCD to make it worth my time. Shooting these handloads in my AR15, I know the self loading process can be a relatively violent one. Crimping the bullet means not having to sweat bullet set back on chambering, nor bullet protrusion from the same event. Also, when I dump 400 fresh handloads into an ammo can, I know the bullets won't be smacked back into the necks from bouncing around. On my loads that use a compressed powder charge, the bullets don't 'walk' out of the case when I use a solid crimp.
The best reason of all to use the LEE Factory Crimp Die.... my rifle is more accurate when I do. Velocity variations are far lower, and this leads to more consistently accurate ammunition. The best accuracy handloads I have in almost every rifle I shoot shows a marked benefit from using the Factory Crimp die. That makes it worth the time.
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34 minutes ago