Hello All
Question for you handloaders about crimping straight walled cartridges to reach higher pressures/velocities in single shot platforms.

Background - Reloading 45-70 with RL7 and 300 gn TTSX bullets in new starline nickle plated brass. 43-44 grains gave good accuracy at ~ 1775-1825 fps. Further increases in powder charge up to 47 grains (~98% load) seemed to plateau in velocity slightly above 1900 fps with larger velocity variations. Before I spend time, energy and money trying investigating this and attempting to increase velocity, I was wondering if any experienced reloaders had any insight. Is this a powder choice issue? A lack of crimp issue?

As a side note, I'm happy hunting with the load that worked,but would like to figure out if I could get a little more out of this platform.

Crimp should help with consistancy, and perhaps with velocity but not likely enough to make all that much of a difference. Barrel length and propellant choice will have a much greater effect on velocity, relative to bullet weight.

I messed around with this using a 460 smith and wesson on a TC Encore Pro Hunter frame with an MGM barrel. I was using H110 and the Hornady XTP MAGs. I maxed out the H110 load, and that is where it was most accurate, or at least very close to max. I backed off a bit to try messing around with the crimp, but couldn't improve the accuracy on what I already had with the near max load.

Just remember, its all fun and games till ya write it down. Then it's SCIENCE!!!

I've noticed something similar to what you described. When I was testing some 460 handloads this spring, I hit a plateau. A 200 grain FTX on top of 51.5 grains of H110 gave me a velocity of 2656 fps and a standard deviation of 27, fps while 52.0 grains gave me 2599 fps and a standard deviation of 54 fps. A charge of 52.5 grains gave me similar results. All loads had a tight crimp, so I just accepted that 51.5 grains was the best load for my gun. On the other hand, back when I was testing my very first 460 handloads, I noticed that applying a crimp to cartridges with minimum loads of H110 increased velocity and consistency. These were both revolvers, mind you, not single shots.

My answer to you is to try out a heavy crimp to see if it make a difference, but only if you feel a 300 grain bullet at 1900 fps isn't quite enough power.

Oh, I'm writing this all down, but my notebook was at home and I was typing at work. I'll load some up with crimps and do some looking for a slightly faster powder to see what works. May be a winter project though.

I do not have any data in front of me, but have you tried H4198?
Yes, a heavy crimp can increase velocity but also increase pressure some. With a single shot pistol a crimp is not really needed. Same with a Ruger #1 But a better propellant would probably benefit you the most.

I don't think a heavy crimp will help that much with RE7. Yes with H110 and a few other powders a heavy crimp is beneficial. A bullet like the TTSX again the crimp will increase pressure and I am thinking that the bad will outweigh the good in this particular case. ( such as accuracy falling off.)
If you are near max or max then back off a grain or a few tenths, chronograph it and look at the results. If not go for it, and let us know.
I have not used this bullet in the 45-70 but I have used it in the 6.8 and found that even with max loads of AA2200 no crimp was better, for velocity and accuracy.

I conducted some trials years ago with a 10" 44 Magnum and 10" 357 Maximum Contender barrel using W296 and crimps. In both barrels my accuracy suffered when I crimped in the bullet cannelure. The biggest surprise was my ES and Standard Deviation was larger when I crimped as opposed to a bullet just seated with neck tension only. Your mileage may vary.

Forgot to mention in my post about the 460 above, this is exactly what I did. Just enough crimp to keep the bullet from pulling out or pushing in using my fingers. My OAL was only .002" shy of the lands and grooves. Put a bullet in an empty case, put it in the chamber of the Encore, then slowly closed the encore to allow the bullet to seat itself into the case. Pulled it out, measured, backed off .002", then set the die accordingly. It worked out pretty good. That gun shoots WELL below MOA, and would hit 300 yards easily. Here is the first of many sub MOA groups I shot with it.