Some years ago I did some extensive testing on a Marlin 44mag rifle with a 1-38 twist. It is clear to me that a 1-38 twist is a carryover from the 44-40 which shot bullets in the 200 grain class. I fired full charge 180 grain, 200's, 225's, 240's, 265's and 300's.
Accuracy was very good with the 180's, 200's and 225's. It began to degrade with the 240's, worse with the 265's and the 300's where actually better than the 265's. But still all of them were sufficiently accurate to kill a deer at 125 yards.
1:20-1:24 is the way to go.
