Yesterday's Weapons Forums

The final step in reloading is the seating of the bullet. Sounds simple, doesn't it? It is if you have done everything else you are supposed to, including proper case preparation.

Before you seat your bullet, you must think about what kind of crimp you are going to use, if any. There are three basic types of crimp, listed and described below.

1. Roll crimp. This is the typical crimp that most reloading dies are manufactured to perform. Inside the die body, there is a little ridge set right below where the bullet is to be seated to it's adjusted depth. When everything is in proper adjustment, the last part of the stroke on your reloading press will push the case up into this little ridge inside the die, and kind of crush, or crimp, the mouth of the case into the side of the bullet. This kind of crimp works best with bullets that have the cannelure formed into the side, a special little serrated groove on jacketed bullets or a simple indented line on lead bullets. Trying to get a proper roll crimp using a non-cannelured (smooth sided) bullet requires that your cases be "dead nuts" exactly the same length or the result will be a lack of uniformity in your crimping from one finished cartridge to the next.

2. Taper crimp. This kind of crimp is often done with a separate die, as a separate step. I think there are some automatic pistol caliber die sets that are now made with this type of crimp in the bullet seating die. This design of crimp does not have the little ridge built in where the bullet is going to be seated, but has a kind of cone shape, or taper, that gently presses the case mouth into the side of the bullet when the bullet is almost fully seated. This type of crimp is most useful on bullets that do not have the cannelure in the sides. It also has the advantage of being somewhat forgiving as to case length, since it won't "accordion" an overlength case like a roll crimp will; it just presses it into the side of the bullet a bit more. Some commercial loaders use the taper crimp routinely.

3. Factory-style crimp. Like the name says, this is a method that some major manufacturers use. Handloaders can get this type of die from Lee. The factory crimp die is done as a separate step after the bullet is seated. It uses a collet to crush the neck of the case firmly into the sides of the bullet. There are a couple of reasons for the use of a factory crimp. One, it gives a nice, tight crimp on the bullet. Two, with a factory crimp, you don't have to be quite as precise with your case trim length as you would with a roll crimp or a taper crimp. I suspect that is why some ammo manufacturers use this method; it eliminates a manufacturing step (trimming). Winchester brass has been the worst for case trimming, in my experience. Not only are they often overlength, but sometimes the case mouth isn't level all the way around; it might have a high side to it. With a roll or taper crimp, an untrimmed case like this would never work properly.

Many reloaders perform the roll or taper crimp process as a separate step, not combined with bullet seating. This is because when you have the press ram up nearing the end of its travel, the crimping process starts. While the crimp is pressing the brass into the bullet, the bullet itself is still moving into place. The bullet seating doesn't stop until the ram reaches the end of the travel. Many reloaders believe that the bullet should be stationary when the crimp is applied.

There is also "No Crimp." If you are going to fire milsurp-pressure cartridges in a bolt action rifle (or single shot) and you have good brass that gives a nice, tight pull (grip) on the bullet, you can dispense with the crimp. Many people who shoot cast rifle bullets don't crimp unless a certain rifle design calls for it.

Applications where a crimp is necessary are:

Rimmed revolver cartriges, particularly magnums (uncrimped bullets can jump forward from recoil and jam the cylinder).

Heavy bolt action calibers/magnums (uncrimped bullets can jump forward from recoil and cause the cartridge to become too long to function in the action).

Auto-loaders and slide action loaders (the violent nature of the action when reloading a fresh round can cause an uncrimped bullet to be shoved into the case).

Lever action rifles with tube magazines (recoil can cause uncrimped bullets to be jammed back into their cases inside the tube magazine).