Deputy Al....that 1-20 .45-70 will handle anything. I've shot everything from the 45791 (mine runs 293 grains) to the grandpa, the #462560 and it runs about 545 grains. No problems with keyholing.

I just rebarrelled the old Springfield to .458 X 2 and I picked a 1-20 twist. Just to be sure, I went back and ran a test with all the big .45 boolits to be sure.

If it was keyholing, I'd suspect it was marginal on size as many of the .458 moulds throw them small. I've had U/S bullets keyhole in a .45/70 Number 1 and also in a .458 Win Mag Number 1 so it happens. Add a little more juice or maybe some dacron and it should straighten right out.

But, getting back to your bullets. Anything should shoot in a 1-20. That Big .45 Bullets article I e-mailed back a couple months ago has my selection in it and they all shoot in a 1-20./beagle

The faster twist and higher velocity of the .458 makes it very easy for cast bullets to strip the rifling and become an unstable blob. At full speed, the bullets need to be hard, but not brittle, and full throat diameter, which should be slightly larger than bore diameter. The larger diameter is needed since the bullets are hard, they have trouble obturating to fill the bore. Gas checks can be very beneficial at these pressures and velocities. Go slowly with wheel weight alloys. The antimony causes them to become brittle which can cause them to chip apart and therefore strip. See why lower velocities and slower twists are easier...

Blackhawk44
I load the 485gr Lyman to MAX loads with WW air cooled. Only slight leading (30 or more rounds) towards the muzzle. Never experienced a cast boolet stripped out - Ruger #1. Biggest problem is verrrry sore shoulder.

I have had good results with an old Lyman 390 gr. RN GC and a Lee 500 gr. RN GC in my Ruger #1 that is a .458 Win Mag that I had rechambered into a .460 Weatherby.

Neal in AZ

Never had a stripping problem so far in the .458 Win Mag that I've noticed. Of course, I've only run the 545 grainers up to 2200 FPS and that was all I needed or wanted.

Use dacron or grex with PB bullets and they shoot just fine. GCs or some kind of base protection is a benefit from my experiences./beagle