The 1:38 twist will stabilize 300 grianers just fine. Add the velocity gain of the 444 over the the 44 and it only gets better. Marlin di make them in 1:38, and those of H&R's floatin' around out there are 1:38. Even in the 444 though, I'd bet that a good study of the ballistic tables would reveal that a 270 grain bullet would hold the edge on velocity, trajectory and retained energy over the 300, and 30 grains of lead ain't gonna make the difference between dead and a long tracking job. Bullet construction is more important than weight. Extra heavy bullets are given more credit than they deserve. The 445 SM will give you 444 starting load level performance or slightly better. The 44 Mag is an exellent candidate for a 444Marlin rechamber