Crimping is one of the most confusing aspects of reloading. All of the manuals “touch” on it. Most don’t give you real direction. They say things like, “Crimp if you want (or need),” “Add the desired crimp,” or “Apply the appropriate crimp.” But they don’t tell you what is “desired” or “necessary” or “how” or even “why!”
This area is so complex, I devote an entire chapter to it in my book, “Things They Don’t Tell You About Reloading” (available through our Marketplace.) But let’s look at the basics here:
There are only two reasons to ever crimp. First and foremost is to prevent bullet creep. What’s bullet creep? That is the effect on any bullet in a gun that is not the one being fired, where the force (usually recoil) causes the bullet(s) to change position in the case(s) still in the gun. So if you fire a round, and the recoil causes the bullet to shift in position in a case for a cartridge still in your gun, that is “bullet creep.” And bullet creep is bad. Period. No two ways around it, and no other way to describe it. Too far in and combustion can rise rapidly. Too far out and it can jam up a gun, refuse to cycle. In extreme cases the bullet can actually come out of the case and dump powder into the action of the firearm!
Reason #2 has to do with the effect of the crimp on combustion. Some cartridges perform better if the bullet movement is retarded slightly at the beginning of ignition of the powder. This gives the powder a split-second longer to more fully combust. This slight retardation of bullet movement can lead to more complete combustion (less unburned powder simply discharged from the gun) and more consistent pressures, which can have a positive effect on accuracy.
Is crimping always needed? No. The one absolute case where it is never needed is when cartridges are being loaded and fired one case at a time. Bench rest competition shooting is an excellent example. In this instance, the reloader (typically the same as the shooter) doesn’t crimp at all. So that reinforces reason #1 above not being needed (you can’t have bullet creep if there are no other cartridges in the gun) and it contradicts #2 above, that crimping can have a positive effect on combustion. Rather, it really confirmed that a crimp doesn’t always improve combustion. Otherwise crimping would be the standard for the most accurate shooters – bench rest – and not not-crimping! But here’s the bottom line: You don’t want bullet creep. So if you have it, you need crimp or more crimp!
There are two traditional types of crimps for handgun ammo. A “taper” crimp is used on semi-auto ammo. It simply squeezes the neck of the case in the area of the mouth firmly against the case. You don’t want the actual front edge of the case disrupted in any fashion because that’s the “stop” for the cartridge to keep it from going too far into the cylinder.
On revolver ammo, a “roll” crimp is used (see picture below). It does what it says – rolls the edge of the case mouth in towards the bullet. The front edge has nothing to do with headspace for a revolver. So that front edge is used to more aggressively or less aggressively grip the bullet. You will note that revolver bullets often have a “crimp groove” for this very purpose. And semi-auto bullets don’t, because you will never “roll” crimp a semi-auto round.
Large caliber handgun ammo can have really aggressive crimps. In this picture, not the case on the far right. It is a very mild 38 Special load and very little crimp is needed to keep the bullet from moving in the case. The middle two cases are 44 Magnum loads, and they have much more aggressive crimps to hold the bullets agains the significantly greater recoil. The case on the far left is a 480 Ruger, and it as the most aggressive crimp of all, because of the exceptional recoil of this round. This last load shoots exceptionally well, and is very accurate. So having more crimp doesn’t necessarily negatively affect accuracy either!
Here are four rifle rounds. All are .308 Winchester. Notice the different type of crimp. It’s not a taper crimp like you would find on a semi-auto round or a roll crimp as would be the case for a revolver round. This is more accurately referred to as a “factory” crimp or a “pinch” crimp. The mouth of the case appears to be “pinched.” The case on the far right is a commercial Remington Cor-Lokt round right out of the box. The “pinch” is very apparent. The second from the right is one of my reloads with no crimp so that you can see the difference. The second from the left is from the same batch of reloads, but with the Lee Factory Crimp die set to a “light” crimp. You can’t see the crimp on this case. But if a rifle-full shoot with no bullet creep, it’s enough. The case on the far left is again from the same batch but with the “heavy” crimp setting. Notice the “pinch” that looks a lot like the Remington factory crimp. That’s Lee’s goal. And that’s why they are called “Factory Crimp” dies. Because the goal is to duplicate the factory crimp.
You will hear rifle reloaders saying they “never” crimp their rifle cartridges. That’s fine if they load and shoot one round at a time. It’s also fine if they have no bullet creep. But if they load that way and shoot them routinely without even checking to see if they have bullet creep… well, that’s not such a good idea!
So, how do you crimp? Historically, people crimped with their bullet seating die. In most instances, you seat all the bullets, move the bullet seating mandrel up enough to be completely out of the way, and then use the body of the die to impart the crimp. That requires a lot of adjusting and un-adjusting of dies to my way of thinking.
So here’s a tip gained from years of experience. Beginners would be well advised to use crimp dies. These are dies that have made a big dent in the reloading die business in the last 10 years. In fact, that’s the primary reason there are now 4-die sets for both rifle and pistol. That fourth die is generally a crimp die. Even if I can only find a 3-die set in the caliber I want, I purchase the crimp die separately and make up a 4-die set myself. Crimp dies are easy to adjust. Follow the manufacturer’s instructions. Generally you will set it up so that the crimping potion of the die just touches the mouth of the case. This is the starting point. From there, you turn the crimp die further in to give you the crimp you want. With my Lee crimp dies, that’s 1/2 turn in for a light crimp, and a full turn in for a heavy crimp. Other brands might be slightly different, but the concept is the same. They are accurate and repeatable. And easy to adjust. And the crimp’s are great. In fact, the Lee crimp dies for rifle cartridges imparts a crimp that’s more like the “pinch-type” crimp that the big manufacturers put on. It’s not a roll or taper crimp. It’s the right crimp for that cartridge.
How do you know when you have enough crimp? Test it at the range. Here’s all you have to do:
- Make up enough rounds with the light crimp to fill the magazine or cylinder of your gun. Take them to the range and bring along the calipers you use to measure C.O.L.
- Load the gun and shoot ONE round. Take the other rounds out and measure them. If there is no change in C.O.L. there has been no bullet creep.
- Here’s an interesting step that most people forget to mention: MAKE SURE THERE IS A HOLE IN THE TARGET FROM YOUR FIRST ROUND! If not, you might have missed the target. But you also might have a squib load (bullet stuck in the barrel.) Notify the range officer and his his/her assistance, unload your gun and check the barrel. (You do NOT want to look down the barrel of a gun at a shooting range without the range officer knowing what you are doing and approving of it!) If there’s no hole and no bullet in the barrel – you missed!
- Reload the gun and repeat. Shoot one round, remove and measure the rest.
- If you finish all rounds with no bullet movement in any of the rounds, then you have enough crimp. You simply don’t need more. You’ve proven the crimp is sufficient at least for that load. Do this each time you increase the powder charge because the higher pressure and velocity could cause bullet creep that wasn’t there at a lower load. Find your ideal load and stick with it, knowing you have enough crimp.
- IF YOU HAVE BULLET CREEP AND YOU STILL HAVE ROUNDS LEFT: Load and shoot them one at a time. If there is only one cartridge in the gun you can’t have any more bullet creep. And you may as well not waste the rounds or go the trouble of pulling the bullets.
- Then repeat the load with more crimp and test again!
Joel Guerin, Versailles, Kentucky