I'm new to shooting 25-20 single shot rifles. I have a Winchester highwall with a 1-10 twist bore. That clearly means shooting heavier bullets. But what about bullet alloys? One "veteran" Wyoming shooter says it simply must be 10-1. Other opinions will be welcome. And yes, I understand that the velocity at which the bullet is driven has a lot to do with such as leading.

I have a Hoch mold for a 105 gr tapered bullet that, so far, seems to be pretty good, and an RCBS mold for a 120 grainer is on its way. How about 90 grainers, gas checks, crimp or no-crimp?

I shoot both black powder and smokeless loads.

Every rifle is different. That Hoch 105 is an excellent bullet to work with. Breechseating or fixed?

Thank you fellers. I also question the 10-1 alloy. I know the 25-20 single shot can be finniky to load for, but that's part of the fun  For now I'm shooting fixed with 4227 and a commercial 115 gr 11BHN bullet. The bullets are not great; I can cast better ones. For my first trial with this bullet I used 8 grains of 4227 and a CCI BR4 primer. Got some leading, not terrible, but a tad more than the usual flecks and skinny strips that can be common. I'll eventually breech seat with this rifle (Wyoming Armory high wall, 1-10 twist). First I've got to find a breech-seater and get the rifle's throat touched up.

Today: cast Hoch 105s with 1-30 alloy, perhaps cut back the powder charge a few tenths. I love this game!!

Bullets are the NOE 120 grain flat-base (258-120-FN) and Mos 119 grain flat-base. Breech-seating only and shooting both 25:1 and 20:1 alloy, the 20:1 alloy gives greater consistency (accuracy). 

Going above this hardness means the bullets are harder to breech-seat and this could deform the bullet.  I am assuming you will be breech-seating, I've never shot either of my rifles with fixed ammunition. 

These are strictly target rifles, although I would love to shoot a few ground squirrels when I get back to the Midwest.