Mt Al
A traditional conversion factor for Black Powder to Smokeless NFB is: 40 to 45% of the BP weight of 4198. Start at the low end and work up. If you are using BP you can use a soft undersize bullet and SPG Lube (or other non-petroleum lube for BP) and the BP will cause obturation to expand the bullet to fit. With Smokeless powder, sufficient obturation usually does not occur so a harder bullet, a couple thousandths over groove diameter, and a common cast bullet smokeless lube (such as 50/50 beeswax/Alox NRA Formula or commercial equivalent) would be appropriate. Cases can be made from 45-90 cases by bending the rims forward with a "button die" and turn to .585-595" then FL size. They will expand 10-15 thousandths ahead of the solid head, but that is usually acceptable because 43 Mauser dies are large enough that the cases will only expand once in that area. With BPCR shooters using 45-90 rifles, these cases are easier to find, cheaper than 50-110 and easier to convert.
Regarding your 9x57R, double rifles that were regulated without a scope often have the regulation altered if a scope is mounted. This may have been your problem.
The above members have given good advice, you would do well to follow it where appropriate.
Mike
