When I started reloading I had three calibers in mind: 9mm, .45acp and .223 Remington. These are the calibers I shoot the most and I had a lot of brass saved up in anticipation of reloading. Many manufacturers of ammunition use a military crimp, or mil-crimp, around the primer pocket. This is a circular stamp that creates a crimped connection between the primer and the bottom of the shell casing. This keeps the primer from easing out of the pocket. This is commonly found on rounds with some sort of waterproofing sealant around the primer pocket, usually military surplus ammo. One common commercial manufacturer that also uses mil-crimps on their brass is Federal .223 in the 100-round bulk packs.
Having a mil-crimp on a pistol round is usually not a problem as the primer seating die will normally just shove the primer right in past the crimp without issue. I would guess that around 1 round in 100 doesn’t seat properly and that is almost always a result of a mil-crimp piece of brass. One notable exception I’ve seen is with Speer brass. I can feel immediately when the primer die tries to set into a Speer case and I stop, back out slightly and remove the case from the priming die and sure enough, it will always say “Speer” on the headstamp.
Unlike pistol rounds, the mil-crimp on rifle brass is a much tougher problem. I’ve certainly loaded a bunch of mil-crimp brass and it can work but the failure rate is much, much higher (I would bet around 25-45% are unusable) and the force required to seat the primers is enormous. This doesn’t do the press any good either.
So, what’s the solution? For many reloaders the simple answer is to cut away the crimp using a reaming tool either manually or by using a brass prep machine like the RCBS Trim Mate Case Prep Center. This does work but the problem is that it involves removing material from the case. The evidence lies in the accumulated brass shavings around the tool. Any time material is removed, the case is less than when the process began. With the high pressures in rifle rounds this is really not a good thing, especially as the brass ages and is reloaded several times.
Another solution that many reloaders prefer is to swage the crimp back from the primer pocket, pressing the brass back into its original form. Dillon Precision has (of course) an ideal tool to accomplish this: the Dillon Super Swage 600. This small, simple device is basically two pivot hinges on a metal base, one housing the brass holder and the other holding the swaging rod. The rod rolls the primer pocket back such that it ends up with a perfectly radiused edge, transitioning from primer pocket to case head smoothly. No material is lost and the pocket accepts primers perfectly.
I bolted mine to the reloading bench on an angle so that the handle comes out and over the edge. This has proven to be a great way to use the device because it is still sideways enough to allow one hand to position the brass and the other to operate the handle while still standing essentially facing the bench. Even though the process is one-at-a-time, the design with its thumb flip case holder and bullet-proof construction is very quick at processing a large amount of brass.
I consider the SS600 an essential part of my reloading system and recommend it to anyone who reloads mil-crimp brass.