If a 300 wthby is free bored what is the max recommended bullet mass? I don't do any free-boring but I've heard that if you do its not a good idea to put the largest possible bullet mass in your loads.

In general, what i've seen, heard, and what I load is a 180 grain bullet. This combination is used by about 95% of all users as the heaviest bullet. probably because the results are fantistic for this cartridge. With the 180 gr load, why would anyone use a heavier bullet? Why not step up to a 340 weatherby and really reach out and touch something.

Especially since a factory-loaded nosler 200 grain bullet can be driven at 3100 fps? I really don't know. I do know in general this caliber is intended to be more efficient with heavier bullet weights than the 300 Win. Mag, but the 165 and 180 grain seem to be the most useful on this continent. I had read about an association between the free-bore design and erratic accuracy, but if it's producing minute-of-angle accuracy at 1000 yards, I don't see how it could be the free-bore design, sounds more to me like improper loads or a barrel defect of some kind. My 300 Weatherby produces excellent groups, I sure haven't seen any erratic accuracy, but I have seen half-inch groups at 100 yards.

I assume the reason is because with heavy bullets the frictional loss in the barrel is greater (thus slower velocities), pair that with the even greater pressure impulse generated by free boring and you increase the likelyhood of breach. I have never heard a reason exactly why you should not use the heaviest bullet, but that is my best guess.