257 Roberts load data

[Huffmanite]

Have a 1891 Argentine mauser rebarreled to 257 Roberts. Gunsmith said DO NOT shoot +P ammo in it. Any one have load data for 87 gr jacketed bullets using H380 or IMR3031 powder.

 

[hivel37]

If you don't have a manual, you may want to go to their websites and get loads straight from the horse.
www.hodgdon.com
www.imrpowder.com
And maybe back off 10% for your purpose.