I've been looking at 6.5 STW load data. The water capacity of the 6.5 STW and the 26 Nosler are pretty close.
STW's often get pushed pretty hard and some of the loads are really fast. I don't know how much pressure these published loads are generating. But, at least it gives a general idea about performance in a very similar round with various powder and bullet combos.
Some of those slow .50 BMG and Vulcan surplus, pull down powders Jeff Bartlett has been selling are no longer available.
DF
