I believe that it's not just the twist but the land configuration as well. I am able to shoot 40's in my 2 cooper 20tac's (12T) and 40's in my 204 with a 12t pacnor, and also in my kreiger barrels, but not in several of my other 12t barrels. I don't know if the differance is 3 grove, 4 grove, 6 grove or smaller or wider lands, but when people say 40's won't shoot in a 12twist barrel, I always ask what brand of barrel first? I have a couple of 11t x-caliber barrels that I just installed and they will not shoot 40's . of course x-caliber is like throwing a dart at a dart board. I will not be buying any more of their barrels no matter what kind of a sale they have. back to 20tac., the 20t or 20p either one, must be my favorite caliber because I have 5 now and I guess therapy is in my near future. as I posted on Saubier, 322 is my go to powder on the 20tac. I think people might be getting carried away with this craze to shoot heavier bullets, it's not like you have just one shot at the varmint. most long shots on squirrels or prairie dogs, you will get a chance to have some follow up. sounds like you found a good load, good luck