130fb is what blackjack uses on the 25x47 and 115fb on the 25 creed. Anything with a .300 neck and around 130fb. Shorter neck, longer freebore. If you send Miles Johnson @ blackjack a message, I'm sure he'll tell you bearing surface lengths, just subtract your neck length from the bearing surface, and that's close to the FB you'll need, add another 20 thousandths or so.This post has lots of pages. It has been a while since I read through it. I would like to know how much if any free bore guys are asking for with the 131 Blackjack?
I've got Retumbo and H1000 but been hearing the RL26 to be the "go too" powder for this cartridge. Also V560/570 on my bench. This is just break in load starting charges I'm looking for. Guessing around 50 grains of either 4831 or RL26. I can get to pressure testing later. Just want a mild deer load for this year using the lighter bullets locally.Those are gonna be too slow