Re: duplicating factory loads??
Replacating a factory loaded cartridge is usually all but impossible, though I did figure out the Remington factory load for the 338RUM 250 grain loads. One reason it can be so hard is because sometimes the factories will use non-canister powders, that means propellents that are not available to hand loaders. If you want a shortcut to a decent load for your rifle you can use the same brand of brass and exact same bullet then choose a powder that gives around 88% load density. That has worked well for me a time or two. Also, if you open a factory loaded round and weigh the powder charge and see if the powder looks familiar you can compare it to a reliable reloading manual to see if something lines up. Good luck and above all be safe!