I'm looking to buy RCBS carbide dies in 357 mag. They offer a roll and a taper crimp version. My 460 mag set says roll crimp and my 45 colt set does not say. I certainly have had no problens with my 460 mag slugs backing out.

What is the difference?


Thanks.

I'm looking to buy RCBS carbide dies in 357 mag. They offer a roll and a taper crimp version. My 460 mag set says roll crimp and my 45 colt set does not say. I certainly have had no problens with my 460 mag slugs backing out.

What is the difference?


Thanks.

roll crimp is a simply rounding the case mouth to hold the bullet securely from moving under recoil. taper crimp is more like clamping the case mouth to the bullet at a 45 degree angle to the case body. i always use a roll crimp, never a problem.

I have always roll crimped revolver rounds. for 30yrs. taper crimp for auto ammo, so it will feed better. roll crimp has less chance of a bullet pulling out, due to recoil.

understood. Thanks

I always roll crimp revolver rounds and it's especially important with high recoil Magnum rounds.

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Since I shoot ICORE and USPSA where reloading time is important I always use a taper crimp. A roll crimp can expand the case neck enough to interfere with a fast reload.

If all your brass is the same length this isn't a problem. With a taper crimp case length doesn't matter as much as with a roll crimp.

I have to wonder how much difference it makes at all. Just one anecdotal example: I wanted to save some money and reload some 500 magnums using bullets with no crimp-ring, so I did and used no crimp at all. Then i marked each one with a sharpie so I could fire one off, then check the others to see if they displaced at all. None of them ever moved at all. And these were full house magnum loads. I don't openly recommend it, but that was also a few years ago when bullets for the 500 were harder to find. I wouldn't hesitate to do more like that for my own personal use.

I have tried to get people to understand this for years without success. The crimp has VERY little to do with preventing bullet pull. The tension of the case neck along the entire length of the bullet seated in the case is what keeps it in place. If you have sufficient case neck tension a crimp is pretty much unnecessary. If you can move a bullet after seating it and before crimping it then the crimp is not going to help, regardless of type of crimp or how much you apply. The expander die button diameter is the key to the problem.

What drail said is true. But, I have to point out that that "very little" contribution that the crimp itself makes in locating the bullet firmly in the case becomes more important as the pressure increases. So by all means employ a good crimp with heavy loads, in addition to making sure your expander/case tension are correct.

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Hmm...interesting point of view, Drail. I have a feeling this topic may be heating up a little. I'm going to stay tuned.

"Drail
I have tried to get people to understand this for years without success. The crimp has VERY little to do with preventing bullet pull. "

I don't think you can get a bullet not to jump in a 340 without a roll crimp. I never could get even a taper crimp, only a roll crimp, to stop bullet jump in my 340

I'm not trying to start an argument here or say that my way is the only way. A long time ago an old timer who knew more about reloading than I ever will taught me about crimping. My expander dies have all had the buttons miked and turned down to the point where when a bullet is seated in the case you can clearly see the outline of the bullet through the case wall. I have taken rounds (with no crimp) and chucked them into an inertial bullet puller and you can whack it hard repeatedly and the bullet does not pull. I apply just enough crimp to remove the flare. I've reloaded heavy, hot .41 and .44 magnum loads and never had any revolver pull the bullets. It just seems strange to me that so many reloaders believe that just a crimp that measures maybe .002" long at only the mouth of the case is going to hold a heavy bullet in place when a heavy recoiling revolver tries to inertially pull it out. I have also had almost no split cases from overworking the mouth by flaring and heavy crimping with this method. I have also made dummy rounds for 1911 work that have been chambered over and over for 10 years and not one of them has ever setback. Measure your expander button and compare it to your bullet dia. If you turn the button down in a drill press or lathe to .0015 to .002" smaller than the bullet dia. the cases will hold the bullet tightly. Try it for yourself. OK, flame suit on.

Drail, I was under the ignorant impression that the standard expander plug was about .002 less than std bullet diameter (I have never measured mine). I have read and heard a much greater difference to the point of not expanding at all. Your suggestion of .015 less than bullet dia seems to little. You are making a very fine point that neck tension is critical and certainly is equally/more important than crimp alone.

What's wrong with my thinking/numbers?

bob

It might be with some dies and might not with others. Assuming your sizing die is reducing the case to its original dia. and that your expander button is only expanding to .002 over bullet dia. you should have a tight grip on the bullet. But for this to work we have to accurately measure the bullet dia.(not what the maker marks them as being) and ensure the expander is not over expanding to the point of being closer to the bullets dia. than we want.
.002 does not sound like much but applied all the way around the bullet it should be enough. (Ever drive a pin punch into a slightly undersized hole? It can be a nightmare to get it back out.) The simple way to tell is to just look at a round after seating the bullet. If you can't clearly see the base of the bullet slightly bulging the case then you need to get more tension. If you want to go tighter than .002 under bullet dia. you can. I don't think that the brass is overstressed from seating a bullet this tightly as it is from flaring and attempting to stop setback by over crimping. I can tell by the feel when seating a bullet if there's enough neck tension. Some brands of brass have different amounts of elasticity when squeezed and stretched. Most of my brass is Federal and WW and they seem to be able to give me consistant results and hardly ever split. Maybe I'm a little off when I say .002", it's possible the difference is slightly more, but the point I wanted to make is control of bullet setback should be addressed with the total tension of the mouth and not just at the crimp. And there's nothing wrong with your thinking.

Right, you don't have to roll crimp as long as you have sufficient neck tension to hold the bullet in place.

But I still do it to get rid of the sharp shoulder that could hang up on the cylinder while using a speedloader. Seating and crimping in two seperate steps will help prevent case bulging and I check mine to make sure they will function right after loading.

Jellybean, I agree 100% with you on every point in your post. I still lightly roll crimp revo rounds just so those moon clips will fall right into place for the Miculek matches.

There is another reason for a roll or taper crimp. Not only to hold the bullet in but to insure reliable feeding. If you don't take off the edge you're bullets may not feed well.

Definately true in automatics but even with revolvers there is a big difference if you shoot competition. The lip on the end of your case would hold up insertion and cause you time in your reloads.

For target practice this is not a problem.

Taper crimp when you headspace on the case mouth. Roll crimp for everything else.

In other words, rimless cases get taper crimped.

In bullseye shooting I use to taper crimp my 45 rounds and I know several in our club used no crimp at all. None of us experienced any problems relative to bullet movement during recoil. Now, shooting full house loads with the 500JRH is another matter. A taper crimp will not hold the bullet from moving forward in the 500JRH revolver. It takes a good roll crimp in the crimp grove to keep the bullet from moving and I might add there is plenty of case tension on the bullet to boot.

I don't use a roll crimp on anything and don't have any problems with bullet movement regardless of the caliber I'm using. Here's some .45 ACP and AR that are at least a step above normal loads and they don't have a roll crimp.



Once you get beyond 50 yards, using a rifle, you can see the improvement in accuracy you get with a taper crimp vs a roll crimp.

There isn't any roll crimp on these .360 DWs and .357s used in a rifle and accuracy is improved.



Here's a 100 yard group shot with the pictured loads.

I use a roll crimp in my magnum revolvers for all of the formentioned reasons, plus I've found that powders like H110/W296, 2400 and Lil' Gun shoot more consistently with a firm crimp.