A Crimp in Time
January 04, 2011
Save yourself aggravation--and worse--with the right bullet crimp for the job at hand.
There was a time, long past, when riflemen engaged in endless debates about crimping bullets, arguing the merits of various styles of crimp, different shapes of cannelures and crimping grooves, and the poundage required to get just the right grip on the bullet.
This was important to them for various reasons. The serious single-shot target shooter paid close attention because the case neck's hold on the bullet was critical to getting the exact pressures required for velocity and accuracy. Hunters using lever-action rifles with tubular magazines paid attention because a proper crimp was vital for reliable functioning, and shooters with hard-kicking rifles needed good crimps to hold the bullets in place and keep them from migrating under recoil.
Today, crimping has become considerably less important for some and completely unnecessary for others. In fact, for some target shooters, a crimp is a detriment, and they recoil in horror at the thought. Several generations of reloaders have come along who regard crimping as a relic of a bygone age, and a large proportion of component bullets now come from the factory with no cannelure at all.
There are still some important applications for crimps, however, and a crimp is one of those things that, when you need it, you really need it.
For example, with the ever-increasing interest in hard-kicking big-bore rifles for many different applications, reloaders are forced to crimp bullets. If the rifle is to be used for dangerous game, the crimp can become a matter of life and death. This applies to both bolt-action and double rifles.
In a bolt action, the cartridges in the magazine take a tremendous beating when the rifle is fired. The recoil hurls them against the front of the magazine box, and the impact can drive the bullet deeper into the case. To see just how damaging this impact can be, take a look at the peened front of a magazine box where it has been repeatedly hammered by big cartridges loaded with solids.
Many a hunter has received an unpleasant surprise when he attempts to chamber the last round from his magazine and finds it won't feed properly or seat in the chamber. This is especially true where a cartridge might find itself in the bottom of the box as the rifle is repeatedly fired, the magazine topped up, and then fired some more.
In Africa, I have seen professional hunters unload their magazines to check the cartridges, and find bullets driven in, hanging out, or moving in the case neck like a toggle switch.
With a double rifle, you have the opposite problem. Under recoil of the first shot, the bullet in the second barrel can migrate forward, striking the rifling. With a real kicker, the bullet can even be driven into the lands and wedged there.
This is no real problem if you then fire the second barrel; pressures will be a little high, but nothing serious. If you attempt to unload the rifle, however, the cartridge may come apart, leaving the bullet stuck in the bore, you holding an empty case, and powder spilled down into the action. That can put the rifle out of commission entirely.
When a cast bullet has only lubrication grooves, as with this .40-65 Winchester, any of them can be used as a crimping groove.
Since the second barrel is usually loaded with a solid and fired less often, the same cartridge may find itself in the second barrel over and over, with a progressive loosening of the bullet.
With a lever-action rifle and tubular magazine, all the same reasons for crimps apply today as they did in 1900. To feed smoothly, the cartridge must be exactly so long--no longer and no shorter. And, because of recoil, the bullet needs to be firmly crimped to keep it from moving and thereby altering the length of the cartridge.
Finally, as a general rule for any hunting ammunition, I like to crimp the bullet if there is a cannelure in the right place (some bullets have more than one). It never hurts to have a crimp, and ammunition gets bounced around, spilled, dumped in pockets, falls on the ground, and is loaded, unloaded and loaded again. All of these activities tend to loosen bullets in their necks. A solid crimp heads off problems.
There are several styles of crimp, and it is difficult to discuss them independently of the different shapes of cannelures and crimping grooves.
Technically, a cannelure is a knurled band around the bullet. It is easy to apply, does not weaken the case appreciably, and accepts any kind of crimp. Its one drawback is that the crimp is not as solid as with a crimping groove, and attempting to apply a tighter crimp can easily bulge the case neck.
Crimping grooves are actual grooves, made either by impressing the jacket or cutting a groove. Cutting removes stock and creates a band of thinner metal, and this can lead to bullet break-up on impact. An impressed groove is usually a radius, where a cut crimping groove is generally square.
The ideal crimping groove is one that in cross-section appears to be a shallow triangle, with its deepest point near the tip of the bullet. It presents a solid wall for the crimped mouth of the case to brace against, effectively preventing the bullet from being pushed into the case. This was a common design on cast bullets and had the added benefit of distinguishing the crimping groove from the lubrication grooves.
The most common rifle crimp is the "roll." The mouth of the case is simply turned inward, squeezed by the seating die or by a special crimping die. Inside the die, the diameter is reduced, and there is an angled transition like a forcing cone. The steepness of this forcing cone determines the shape of the crimp. This style of crimp has the advantage of working with virtually any style of cannelure or crimping groove.
Redding makes a special die that applies a "profile" crimp. This forms a taper, ending in a tight, uniform roll crimp. It is intended for blackpowder target shooters, where ignition and consistency depend largely on uniformity of crimping. However, it is also ideal for cartridges used in a tubular magazine.
Another style of crimp, rare in civilian circles, is the parallel crimp. Instead of simply turning the case mouth inward, an entire band of the case mouth, perhaps 1/32nd o
f an inch wide, is pressed into the crimping groove. This prevents the bullet from moving either forward or back and gives the case an iron grip.
It was the standard approach for machine-gun ammunition, where cartridges take a terrific pounding whether in belt or box, and where durability is critical. For the average handloader, even one loading powerful dangerous-game cartridges, such a crimp is not necessary.
Finally, there is a style of crimp that is almost completely forgotten, in rifle ammunition at least: the neck crease. When the bullet is seated, the cannelure is hidden inside the neck. A special tool is used to imprint a crease in the neck, pressing it down into the hidden cannelure. This was common with Kynoch cartridges loaded with jacketed bullets.
Cartridges for lever-action rifles must be held to an exact length in order to function through the action and feed properly. A firm crimp is required to prevent the bullet being driven back into the case under recoil.
We still see such crimps on handgun cartridges, both semiauto and revolver. Handloaders view them with a jaundiced eye because they mar the brass and can weaken it, but they are effective crimps.
Applying a crimp is not difficult, but it does require attention to detail. We will assume you have chosen the correct bullet, and you know the crimping groove is in the right place to give you the desired overall cartridge length.
Next, you need brass sized and trimmed to the exact same length. Brass that is a touch too long or too short will not give you an optimum crimp and can cause real problems.
With a seater die that has a crimping function, the next step is to carefully seat the bullet to the exact depth you need, with the die backed out enough that the crimping section does not come in contact with the case. When the bullet is where you want it, you back the bullet seater out to a safe distance, raise the turret to its maximum height with the cartridge inside the die, then screw the die down until the crimping area comes into contact with the case mouth.
Redding makes special "profile" crimping dies for blackpowder competition cartridges that apply a gradual taper coupled with an exact roll crimp.
This is where it becomes somewhat delicate. Lower the turret, tighten the die one-half turn, raise the turret to maximum, and then inspect your crimp. If you want it tighter, rotate the die in another quarter turn. Continue until you have the crimp you need.
At that point, tighten the lock nut on the die, raise the cartridge all the way into the die, and screw the bullet seater down until it comes in contact with the bullet nose.
Finished? Not quite. Inspect the crimp and neck closely. Run your fingers over the case neck, checking for the slightest sign of a bulge. English gun makers refer to craftsmen having "eyes in their fingertips," and the best way to check for problems like this is to run your fingers over the bullet and neck, twirling the cartridge in your hands. Your fingers will detect tiny flaws your eyes might never see.
If it is possible to do it safely, run the cartridge into the rifle chamber to ensure it chambers easily.
Now, carefully prepare a second cartridge, checking it every step of the way as you seat the bullet to ensure each adjustment is correct. Sometimes, tightening the lock nut will throw the die off just enough to affect your overall seating depth, the location of the cannelure and, of course, the crimp itself.
If you are working with a separate crimping die, follow all the above procedures, except ensure the seating die's crimping area (if it has one) never comes in contact with the case mouth.
A crimp can be only so tight and no tighter. If you try to apply a crimp that is too heavy, you run the risk of bulging the case neck. Such a bulge may be barely visible to the naked eye, but it can prevent the cartridge from chambering. As well, even the slightest expansion will reduce the neck's grip on the bullet, leaving it held in place by only the crimp. Not good. This can occur with both bottleneck and straight cases.
Many features found on bullets in the 1890s are making their way back, their virtues rediscovered a century later as riflemen return to the world of cast bullets, blackpowder, big bores and heavy recoil. The driving bands on the Barnes Triple-Shock bullet and on Federal's redesigned Trophy Bonded Bear Claw are examples.
Barnes Triple-Shock and Banded Solids have square-cut crimping grooves, allowing an extremely tight and solid crimp. In special situations they can be seated farther out, using one of the rear grooves for crimping. From left: the new Nosler Solid .416 with a square-cut crimping groove; a cast .416 from Huntington Die Specialties; and a Hornady .458, with a knurled cannelure.
The same is true of crimps and cannelures. After decades of being consigned to the shadows by the uber-accuracy crowd, they are reemerging and proving their worth in hunting circles all over again.
The difference between now and 1890 is that we are working with jacketed bullets and bolt-action rifles. With bolt actions, we are accustomed to great freedom in seating depth, overall cartridge length and a wide choice of bullets.
Recognizing the importance of cannelures, some manufacturers are now offering bullets with or without them; others are putting two cannelures on a bullet to accommodate different seating depths, still others offer special-order cannelures anywhere you want them.
For casual shooting and hunting close to home, this may be a lot of trouble, but when you are half a world away with something big lurking in the bushes, a firmly crimped bullet can be worth its weight in gold.