45-70 help

[BD]

Could one of you 45/70 loaders tell me the length of a .458 300 grain RNFP? How about a 500 grainer? Any thoughts on optimum twist for the 300 grainer at 2,100 and the 500 grainer at 1,800?
BD

[TGM]

The ones I cast are as follows:

Lyman 457191 300 gr.RNFP .785
Lyman 457125 500gr RN 1.314

Ruger and Marlin 45-70 rifles have a 1 in 20 twist rate.

TGM

[BD]

Thanks TGM. This is off topic for "leverguns" but I didn't get any response to the same query on Cast Boolits". I figured someone on this forum would have a couple of examples laying in front of them on the bench. I'm looking into a .45 AR and I've noticed that the .450 bushmaster is generally built with a 1/24 twist while the .458 Socom is generally a 1/14. I am wondering which would make the better cast boolit launcher. I'm looking at the Greenhill formula and resulting rpms. The load I'm really after would be a 300 grain version of the BDacp at around 2,000 fps.
BD

[crabo]

BD, let us know what you come up with.

[Mumblypeg]

BD, RCBS 300grn GC .830" , 500grn Hornady J ( don't have a 500gr cast) 1.333".

[BD]

My calculations indicate that the 300 grainer in a .458 would need a 37.9 twist, in the .451 it would need a 36.7 twist. The 500 grainer in a .458 wants a 23.9 twist, in the .451 it needs a 23.2 twist.

This leads me to the conclusion that the .458 socom with a 14 twist will easily stabilize anything I may care to shoot. However, the .450 bushmaster with it's 24 twist is right on the edge of not stabilizing the 500 grainers.

I'm left wondering if the much faster twist in the socom might make accuracy harder to achieve with cast? It would have the 500 grainers at 1,800 fps spinning about 92,000 rpm and the 300 grainers at 2,000 fps spinning about 103,000 rpm. Seems like lighter bullets might get to be an issue if you tried to push them to the top end.

BD