Crimping bullets in place when handloading the .223 Remington came up in a conversation the other day, making me think it might be worth a blog post. But first, just in case you’re new to reloading, let’s define crimp as: pinching or squeezing an object in order to prevent something from moving (the photo at left shows a crimp).
Shooters of ARs inevitably run into the question of whether or not to crimp, so here’s my take on the question.
To address it effectively, you have to remember the purpose of crimp and understand that bullets can be set back into a cartridge case when subjected to a violent trip from magazine to chamber. This happens most often with semiautos, but can occur with bolt rifles as well. This set-back is a bad thing because it effectively reduces case capacity … and that can cause dangerous pressure spikes.
It’s easy enough to test your reloads by measuring the overall length of a loaded .223 Rem. cartridge and then letting the rifle’s mechanism feed it quickly from magazine to chamber a few times. If the rifle has detachable magazines, do this with every magazine you’ll use in the rifle. If the cartridge’s length doesn’t change, a crimp isn’t necessary. If it does change, apply a crimp and test again. Keep increasing the crimp until the cartridge length doesn’t change.
But there’s another reason to crimp, and that’s to increase accuracy. I’ve found that after developing a reload for any rifle, it’s always worth trying the same load again, but with a medium crimp. Sometimes a simple crimp can shrink groups. One semiauto rifle I load for fits in this category. I crimp Nosler 60-grain Ballistic Tip bullets into Remington cases because it increases accuracy.
Conventional reloading dies apply a roll crimp, which as the name implies rolls the mouth of the cartridge case into the bullet. If you use this type of crimp, it should only be applied to bullets with a cannelure. Another alternative is a crimp applied with LEE’s collet crimp die. This design can be used to crimp bullets without a cannelure, making it more versatile; it’s the die I prefer.
LEE’s Factory Crimp Die is a collet die that does a great job of applying crimp.
One additional bit of caution relates to applying too much crimp: I’ve had .223 Rem. cases bulge imperceptibly at the neck when this happens, which can cause difficult chambering. I’ve seen semiautos successfully feed these cartridges, thanks largely to a stout recoil spring, but unfired cartridges become extremely difficult to extract. It’s not a bad idea to measure neck diameter before and after crimping to make sure you’re not bulging the neck.
So, in summary, you must crimp if cartridge overall length changes as a result of feeding from magazine to chamber. If not, crimping is optional, but it’s worth trying a light crimp just to see if it improves accuracy.