Crimping Handloads - Inside MDT

Posted by Al Voth on 2023 Aug 17th

Crimping Handloads - Inside MDT

Crimping bullets in place when handloading cartridges can be a controversial topic, which makes it worth examining. But first, just in case you're new to reloading, let's define crimp as pinching or squeezing an object to prevent something from moving. In handloading, crimping is squeezing the case's mouth to prevent the bullet from moving prematurely.

To address the topic effectively, we must understand that once a cartridge is in a firearm, bullets can be set back into a cartridge case in several ways, and it's universally a bad thing. Of course, the degree of setback matters, and that depends on cartridge design and dimensions. It's always bad news because it effectively reduces case capacity, which in turn can cause dangerous pressure spikes. But it can also affect accuracy because it plays havoc with having uniform overall cartridge lengths.

A common cause of bullet setback occurs during a firearm's feeding cycle when the cartridge is stripped from the magazine and fed into the chamber. If the nose of the bullet doesn't make the trip smoothly and without interference, the entire bullet can be pushed back in the case. This is most commonly seen on semi-autos because of the speed at which the bolt cycles. But this magazine-induced setback can occur with other action types if the rifle/magazine interface is not properly tuned. High-quality magazines like those in the MDT line will go a long way to preventing this.

Many factory loads are crimped with a variety of styles used.

It's easy enough to determine if handloads are being shortened via magazine feeding by measuring the overall length of a loaded 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 used in the rifle. If the cartridge's length doesn't change, a crimp is unnecessary. If it does change, apply a crimp to a fresh cartridge and test again. Keep increasing the amount of crimp until the cartridge length doesn't change.

Cartridge length can change as a result of recoil as well. This is especially prominent in lever-actions with a magazine tube. The combination of the force exerted by the magazine tube spring and the inertia of recoil will quickly shorten cartridge overall length, making a sturdy crimp absolutely necessary. Likewise, for hard recoiling bolt-action rifles with box magazines, only here it's the cartridge nose slamming into the front of the magazine box as a result of recoil, which does the damage.

Feeding a cartridge from a magazine into a chamber can be enough to change its overall

length.

CRIMPING AND ACCURACY

But there can be another reason to crimp: to increase accuracy. After developing an accurate load for any rifle, it's often worth trying the same load again but with a light to medium crimp. Sometimes this can shrink groups even further. One semi-auto rifle I load for fits in this category. For that gun, I crimp Nosler 60-grain Ballistic Tip bullets into Remington cases because it increases accuracy.

Adjusting neck tension for optimal accuracy is a rabbit hole that shooters looking for extreme accuracy often wander down. Usually, it's done via the use of match-grade dies, which use bushings of varying sizes to adjust how much neck diameter is reduced when case re-sizing is done. Using a smaller bushing which therefore provides greater neck tension, is a good way to avoid having to crimp. However, these match-grade dies, and a collection of bushings can be expensive.

Dies using interchangeable bushings to adjust neck tension can negate having to crimp.

Conventional rifle 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, and it's the die I prefer.

Many people don't realize factory centerfire rifle ammo is often crimped. Certainly, it's most common with cartridges the factory expects may be used in a semi-auto rifle or one with a tubular magazine. Military ammo is almost always crimped, or a sealer/glue of some type is used to prevent bullet movement and keep out moisture. Considering the rough handling and full-auto use which military ammo is subjected to makes it easy to understand why this is done. Whether civilian or military, a close look at the mouth of the neck will show if it's crimped or not.

LEE's crimp die uses a collet to apply crimp.

One further caution relates to applying too much crimp. I've had .223 Remington cases bulge imperceptibly at the neck when crimping too much, and it's caused me problems with the chambering and extraction of unfired cartridges. I've seen semi-autos successfully feed these cartridges, thanks largely to a stout recoil spring, but unfired cartridges become extremely difficult to extract. It's always a good idea to measure neck diameter before and after crimping to ensure the crimping process isn't bulging the neck.

So, in summary, crimping is essential if the cartridge's overall length changes due to recoil while cartridges are in the magazine or via feeding from the magazine to chamber. If not, crimping is optional, but sometimes it's worth trying a light crimp or increasing neck tension via a bushing die to see if it shrinks group size.

CALIBER RESOURCES FROM MDT

ABOUT THE AUTHOR

Al Voth calls himself a "student of the gun." Retired from a 35-year career in law enforcement, including nine years on an Emergency Response Team, he now works as an editor, freelance writer, and photographer, in addition to keeping active as a consultant in the field he most recently left behind—forensic firearm examination. He is a court-qualified expert in that forensic discipline, having worked in that capacity in three countries. These days, when he's not working, you'll likely find him hunting varmints and predators (the 4-legged variety).

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