Cast Bullets: Lite crimp VS Heavy crimp?? (in REVOLVERS)

[Southern Shooter]

I work with cast bullets in my reloading. And, I continually hear about "lite crimp" and "heavy crimp" to effect powder and bullet performance.

My questions are:

What do the two look like?

How can you disguish between the two?

When would you use one type versus the other?

What is the effect of one type versus the other?

Thanks.

[hornetguy]

If you are talking about handgun loads for revolvers, the amount of crimp applied to the cartridge is a function of how far down in the press you adjust your seat/crimp die. The crimp is formed by a slight radius that is machined into the inside of the die. The further you push the case up into the die, the more the radius "rolls" the mouth of the case into the cannelure (or crimp groove in a cast bullet). A light crimp will only slightly roll the edge inward, and a heavy crimp will visibly curve the mouth of the case into the crimp groove.
A heavy crimp is necessary for heavy recoiling loads, to keep the bullet from being pulled forward (through inertia) when the gun is fired. A heavy crimp also helps in gving slow-burning powders a chance to get burning well before the bullet starts moving down the bore.
That's some of it, in a very small nutshell... One could write a pretty nice chapter in a book just on bullet crimp and what to watch for, so don't hesitate to ask for clarification, or just more general information. Hope this helps a little bit.

[PawPaw]

Not to be obtuse, but the answer is: It Depends.

It depends on what kind of handgun you're shooting, or even if you're using cast bullets in a rifle. Semi-autos generally don't get a crimp, simply use enough to iron out the flare you put in the case before seating the bullet. Revolver loads get a crimp, sufficient to keep the bullet from moving forward out of the case in recoil. If you've ever had a heavy bullet in a heavy load "jump the crimp" and tie up your revolver, you'll understand the need for a heavy crimp on revolver loads.

In rifle ammo, it depends on whether you're loading for a tube magazine, like the .30-30, or a box magazine, or if you're shooting a single shot. My .45-70 loads for my Sharps get a medium crimp to hold the bullet for just an instant as pressure builds. My .30-30 loads get a heavy crimp to avoid setback in the magazine under recoil. My .30-06 loads don't get a crimp at all.

What do the two look like? That comes with experience. You'll figure it out. I use a cheap loupe to look at the crimp when I'm setting up my dies. Magnification helps my tired old eyes.

[dahermit]

Many hand loaders use too much crimp. Excessive (any more than you need), crimp shortens case-life.

As a rule of thumb, look at the crimp applied to factory rounds. If they needed any more crimp than that, the factory would use more.

The perceived need for a heavy crimp, in most cases is more than what is actually needed to keep the bullet from moving in the case under recoil.

[Scharfschuetzer]

A uniform case length will also help keep your crimp uniform. Longer cases will get a heavier crimp than short cases when run into the crimping/seating die.

I just load my cast pistol bullets to a moderate velocity (for calibre) so I use a moderate crimp. It's by eye though. I have no idea how it could be measured in foot pounds or pressure needed to dislodge a bullet.

[243winxb]

Only one crimp. Roll for revolvers till the brass contacts the bullet in the crimp groove. Taper crimp for autos just a little more than taking the bell out or till the round will chamber. But not more than .001" under case body diameter. Some photos of over crimping > http://www.photobucket.com/joe1944usa

[Mike / Tx]

I'll throw in my .20 as well. (used to be only .02, but that really ain't worth much to anyone anymore.)

When I started loading for my revolvers and then my auto's I found that while some may defend to the death that trimming handgun cases is meaningless, and trivial. In my evaluations of both trimmed and untrimmed cases, my trimmed cases not only preformed better in shot to shot velocity spreads but were also more accurate. This said while there are folks who strive for accuracy in a rifle, quite a few of these same folks may never realize the true potential of their revolver or pistol. There is no way possible to ensure the crimps are uniform with out trimming period. If one has more than the next they will develop different pressures, and you will get fliers. While some folks might be happy putting shots into groups of 3" at 20yds, I am not happy unless they are around 1" and certainly less than 2".

Also where tons of folk say to put a heavy crimp on heavy bullets and higher powder charges, a lot of them fail to take into consideration the actual case tension which is also applied when everything is set up properly. Just like in a rifle load case tension is also and should be included in your criteria.

When I start to work up a load, even for my 454, I start out using as light of a crimp as possible and then work it down until I get it to just hold the bullets then only a touch more. I start out with a full cylinder, and shoot the first round then inspect the others for any amount of creep. I then remove the fired case and load a fresh round into that chamber and fire another, again checking the rest for any amount of creep. If after 6 consecutive rounds, I have found nothing moving I consider that good enough for the time being.

I then will set up the chrony and check velocities to see where they are in regards to the load I am using and work it up accordingly. As I work up I also check the last round in the cylinder to see if anything is changing as I move ahead. If I find something slipped, I adjust the crimp a bit more, not a lot, but simply enough that I actually know I turned the die. I usually mark my press and dies with a fine point Sharpie, at 12, 3, 6, and 9 o'clock, and then put a mark on the seating stem, and top of the die as well to allow a bit if fine tuning.

Case in point, on the left is my friends loads that he set the crimp on and then griped about how they weren't accurate. On the right are the same loads, same brass, shot out of the same gun, only the crimp was backed off slightly. Both groups were shot off hand at 40yds,


Another group fired off hand at 25yds with my 454 using the posted bullets,



or this one,


While I do not consider myself any sort of a great shooter, I DO strive to produce accurate ammo, and have found a few things which work along the way. The crimp issue has helped me dial in more than one load in really quick fashion. It sounds WAY more complicated than it really is. I use my handguns for hunting mainly and my shots are usually starting out at 25yds and may go out past 100 depending on the terrain. I am mostly hunting feral hogs with them, but will not hesitate to reach out on a yote as well. Granted I am not NEARLY as practiced at 100yds as I would like to be, but I work on it every chance I get. I do however have quite a few groups of 1" or so at 25yds and a few out to 50 shooting offhand. Rested groups are fairly good as well, but most of the hunting doesn't allow that as it happens fast and there isn't time. All in all though my last hog hit the dirt at 87yds DRT with the first shot.

I have found with lead bullets, they require a bit more crimp than their jacketed counterparts. This is in part due to the fact they are a bit more slippery, and the added lube don't help. This said however, I have also found that once the crimp is set, it usually isn't much more than it would be using a jacketed, and surely not one of those which looks like I was trying to swadge the case into the bullet like some I see.

Hope this helps, it has proven time and time again to work for my needs.

[Scharfschuetzer]

Mike,

Great tip for checking on bullet crimp and case tension for a revolver. If I ever load up my magnum revolvers to their full potential again, I will definately use it.

Back in my PPC competition days, all my 50 yard loads had to shoot into 2" or less or you just weren't competitive in the higher classes. Trimming those cases was a step I took to ensure their accuracy and so they would hold the X and 10 rings.

[totaldla]

Take a look in the crimp section of the 329pd info. Hope this helps.

[Scharfschuetzer]

Great article on the S&W 329 (Airllight 44 Mag) Totala. Having never shot one of the Airlight aloy framed revolvers, I found the article most illuminating.

Those ultra light pistols present some unique issues and, as you note, require a very heavy crimp as well as a uniform crimp for best performance.