How much crimp?

[REDLINE]

After pulling some factory ammo last week (as posted), most loads were crimped enough to easily noticeably see the bullets deformed from the crimping stage.  My calipers show enough crimp to lessen the bullet diameter up to .005".

Is there EVER a good reason with 10mm ammo to crimp so much as to deform the bullet?

[DM1906]

.005" bullet bite isn't necessarily a bad thing, or necessarily significant.  With the 10mm, you have to treat it like most magnum rounds, and the neck tension and crimp are important.  It's more difficult to get a firm bite with a taper crimp, so it does need to bite a bit with many loads.  Lighter bullets/loads aren't as critical, but heavier bullets with heavier charges are.  If you are using quality bullets, and a good crimp die, you can keep this to a minimum, and there will be no loss of accuracy.  It is important, however, to seat/crimp full power rounds in separate steps, or more significant deformation will occur to get a good crimp (bullet is driven into the started crimp, as it's crimped), and is necessary for consistent performance.  The Lee Factory Crimp Die does an excellent job of this, offering a very consistent crimp, round to round, and requires you to separate the process.  It doesn't necessarily make a better crimp than a high quality die, but is dedicated to the chore.  An added bonus is you can true cases all the way to the rim with it (bulge-buster feature).

[REDLINE]

So with the 10mm Auto, crimping is not just for removing case flare manually created for inserting a bullet into the case?

[gmtmaster]

I dont crimp

[REDLINE]

I dont crimp

Are you saying simply removing the flare for seating a bullet is different than crimping?

[The_Shadow]

I seat the bullets to depth in one step, then in a seperate step I run them in a tapered crimp die, while I don't really measure the amount I test that the bullets don't move in or out or able to spin inside the finished casing.  Seeing how the case is headspacing on the case mouth mostly, not over doing the crimp helps.  I like to see a shine on the edge of the case mouth where the taper is squeezing the edge inward.

Too much crimp can cause the bullet to move in/out or spin and even buckle the case, increasing the diameter none of which is a good situation.  However too little crimp and the bullet could also move and set up a bullet setback issue.

[sqlbullet]

IMHO....

Proper neck tension is achieved by how the mouth is expanded during neck flare.  The crimp step is only to remove whatever flare you needed to start the bullet.

If you need more tension, you should turn down the insert into your flare die.  If you need less then you need to order a larger one.  RCBS and Lyman will sell you ones in increments of .001" as I recall.

[Taterhead]

I am of the opinion with straight-wall cases the most important element is neck tension. I have not found crimping to have much impact on bullet pull. Accordingly, I crimp just enough to remove the bell. The outside diameter of my crimped cases when using Starline brass is about 0.422".  I have found that excessive crimping can actually cause the bullet to have less bullet pull.

Just today I finished pulling down about 250 .40 S&W rounds that were reloads by an unknown source. They appeared to be new brass, and I pulled them to re-use the components (I don't make it a practice of shooting another person's reloads).  The person that loaded these gave a substantial  crimp such that it slightly "mushroom topped" the bullets in some instances. The bullets that had the most sever crimp ironically popped out the easiest with the kinetic puller. Excessive crimping re-sizes the bullets to a narrower diameter. The brass will have a tiny bit of spring back so the narrower diameter bullet will afford less grip. The bullets with less crimp and less bullet engraving were more difficult to pull. I consistently observed that more crimp = less bullet pull.

Also, work-hardened brass will have minimal neck tension. This cannot be overcome with a tight taper crimp. Again the heavy crimp narrows the diameter of the bullet, the brass springs back some, and there is an impaired grip. I have had work-hardened 10mm cases that can be "setback" with thumb pressure. No amount of crimp with address this problem unless you crimp to the point of crimping the bullet into the shape of a mushroom head.

In my opinion, taper crimping should just barely remove the bell and not engrave the bullet. A clean finish is paramount for feeding in an autoloader. The accuracy of some bullet types (especially plated) can be impaired by engraving from taper crimping.  Bullet setback is a function of neck tension (or lack thereof) from a properly sized and not work-hardened case. Some of the slower powders used in 10mm auto like high bullet pull. Too much crimp can impair bullet pull. I can see how a big mushroom head can help with setback, but the undersized bullet will affect bore-to-bullet fit and bullet pull.

[REDLINE]

Thank you all for the excellent replies!

[REDLINE]

I have had work-hardened 10mm cases that can be "setback" with thumb pressure.

Can I pretty much assume that should never be an issue with new brass assuming all other handloading steps have been done properly?

[sqlbullet]

That i correct. And, I would bet 90% of the brass that is work hardened enough not to resize would probably have split on the next load anyway.

I thought I had this issue once right after I got my pass through size die.  But in fact it was that a pass through doesn't size the case mouth very well.  I had sized with the pass through and deprimed with the universal decapping die, skipping the sizing doe altogether.  Ran them back though the sizing die with the decapping pin out, since they were primed, and they were good.

[Taterhead]

That i correct. And, I would bet 90% of the brass that is work hardened enough not to resize would probably have split on the next load anyway.

I wondered the same thing, so I loaded up 12 - 15. I single fed them from a magazine: Loaded one round in a mag and gently racked the slide. Bang. Repeat. None of them split. I was a bit surprised. Too hard for neck tension, but not hardened enough to split. Mostly brass does not split in my G20. It shrinks too short most of the time, and that is the limit to case life in my big G20 (other than losing them of course).

This thread just reminded me of something that happened recently. I was helping a first time shooter at an IDPA match earlier this year. First time I have used my squib rod. He had a 45 auto that was having bullets stuck in the throat when attempting to clear his gun. I at first suspected too long COL. Not the problem. He had some pretty "rode hard" looking brass. What was happening was that the bullets were jumping forward out of the case when chambering. The case would stop forward travel, but the bullets would keep going and get stuffed into the barrel enough to stick a little bit. When trying to clear, the case would come out without the bullet, and powder spilled everywhere.

He was giving a pretty good crimp, but it wasn't helping the problem. You could setback bullets without too much effort pushing against a bench. Solution? Even 45 auto brass has a limited shelf life.

[sqlbullet]

To bad it is so hard to anneal short straight wall cases.  That is really what they need.

[REDLINE]

I wondered the same thing, so I loaded up 12 - 15.

Just to be clear, those "12-15" were at least once-fired and not resized?

[Taterhead]

I wondered the same thing, so I loaded up 12 - 15.

Just to be clear, those "12-15" were at least once-fired and not resized?

Yes they had been reloaded a few times. They were, however, resized. I had loaded them with 150 grainers. Bullets could be pushed into the case with my thumb! I fiddled with crimp, but that helped not at all. I pulled those bullets, resized with the decapping pin removed, lightly flared, and then loaded them with 200 grain bullets. The longer bearing surface helped a little, but still not satisfactory neck tension. No splits upon firing.