TargetTalk

This is about taper crimping cases onto .32 and .38 lead wadcutters, for target work. I'd expect jacketed bullets to behave differently.

I'm puzzled about the mechanics of taper crimping. Lead behaves much more plastically when compressed, compared to brass - lead has very little elastic deformation or recoil. Brass, even well annealed (which cases usually aren't) behaves much more elastically than lead, and springs back after deformation. For example, after re-sizing, the case's outside diameter springs back to be just a tad larger than the die's inside diameter.

If a bullet with a diameter a bit larger than the case's inside diameter is forced into the case, the lead will be compressed, but, in so doing, will expand the case a little. The case will therefore continue to exert a radial force on the bullet (reacting the bullet's expanding force on the case) when removed from the die, and so will grip the bullet (although perhaps not very firmly).

But if the case is taper crimped, ie compressed around the seated bullet, surely, when pressure is removed, the case will spring back (perhaps only a gnat's), whereas the lead will remain plastically deformed, reduced in diameter. How can this result in a useful degree of grip?

The part of the bullet under the crimp gets squashed permanently, the main part behind will stay its original size.
On firing the main part of the bullet has to force its way past the taper crimp, creating a reasonably predictable force which needs to be overcome - hence a consistent start pressure for each shot.

More consistent than trying to rely on diameter difference between bullet and case to give consistent friction.

Taper crimp should give a start pressure less dependent on case length than roll crimp.

Another purpose of taper crimping is for cartidges that headspace on the rim. A taper crimp is necesary versus a roll crimp because a roll crimp, especially if overdone, will affect how the cartriddge is aligned in the chamber. I find as small a taper crimp that I can get with the case still champbering freely is when I get the best accuracy.
Ted

Hello,
I have loaded over 500,000 hollow-base wadcutters in 38 SPL. I put a very mild taper crimp just enough to allow proper feeding in my auto and enough to drop into my revolver with no pressure. I do not think you need to worry about the characteristics of the lead wadcutter.

I have shot loads through a Ransom Rest testing accuracy and the light loads I use are more accurate than I. Crimping FMJ or JHP bullets is slightly different. Typically, there is a crimp groove in the jacket where you crimp. Jacketed bullets are normally driven at a higher fps than wadcutters. As such you need enough crimp to keep the bullet from moving in the unfired cylinders of the revolver.

The bullets that will distort are the TMJs with a smooth side - no crimp groove. When you crimp those you will distort the bullet. In fact, seating the bullet also distorts any bullet as the walls of the cases are not exactly the same case to case.

However, I do not think you need to worry about most of this. Use a light crimp and go to the range. The proof is in the holes on the paper in and around the ten ring.

Remember, the headspace on a 38 Spl is on the rim. In the years I have spent reloading millions of rounds I have avoided roll crimps.

Taper crimping has been very good to me. I have used different dies over the years preferring the Lee taper crimp or factory crimp dies. They have a very nice feature for finishing the loaded round to factory specifications. Good Luck.