walstr wrote:the Redding 45-70 die set does a good job of RESIZING my neck area on the way to a 'roll' crimp.
Unfortunately, that is a common problem these days. Not just Redding, though you're not the first to complain about Redding dies squishing the loaded cartridge.
You seem to share my interest in doing experiments and learning how things work. I appreciate your detailed information, I wish all my customers would post stuff like that.
The left side is more or less correct, the right side is incorrect. If you want a flat bottomed groove then I suggest crimping in a lube groove rather than a crimp groove.
I can't see all of your pictures -- not sure if there is something wrong with the way you posted them, or if my ISP-from-hell is timing out trying to load them? Apparently I can see the ones that are attachments but not the ones that use the "IMG" tag. The IMG tag is for photobucket or other pictures stored on the web, the procedure is:
Your Beartooth bullet appears to have a puny crimp groove, puny both in length and in depth. That could be part of the problem. My crimp grooves are the same depth as the lube grooves -- 0.417" diameter in your case.
Another factor in bullet retention, a very important factor, is neck tension. This can depend partly on the brass -- some brass has better "memory" than other brass -- and partly on the expander plug diameter. The typical expander plug, as it comes from the factor, is too big, reducing case neck tension. Off the top of my head, I can't remember the optimal expander diameter but want to say 0.006" - 0.010" less than the bullet diameter. And it will vary depending on the bullet alloy.
A soft bullet requires a bigger expander plug than a hard bullet, because excessive neck tension can squash a soft bullet when it is seated (pull a bullet from a dummy round and measure it to see if it was squashed). But it as long as it is not squashed, there is no harm in having lots of neck tension. Neck tension provides about 50% of the grip on the bullet, if not more.
Also, seating dies that squish the cartridge seem to reduce neck tension -- yet another reason to avoid those seating dies.
I don't shoot a 45/70, so I can't speak to that cartridge, but in my Marlin 357, I use a very light crimp. It's more of a "tuck" than a crimp, simply tucking the flared case mouth in slightly. If I didn't "tuck" the case mouth, it would present a sharp edge that could interfere with chambering. So it's the neck tension that is doing most of the gripping, and I haven't had any problem with bullets moving around in my Marlin.
Revolvers, on the other hand, need a "hard" crimp and lots of neck tension to prevent the bullet from "walking out" under recoil. I have had bullets "walk out" in 44 mag revolvers, even with a hard crimp. With one gun/load combo, the only way I could keep the bullets in the case was to use newer cases or to anneal the necks on old cases. Otherwise the older cases seemed to lose their "memory" and would not grip as tightly as new cases.
I will try to post a pic of my 357 Marlin ammo tomorrow, to show how I crimp it.