Did one test barrel, identical to the STW in same length barrels. In fact seems to produce a bit less pressure at same velocites with same bullets but that goes to reason as it is a bit larger in case capacity.
Powder bridging is an issue still. Not to the degree that the Allen Mag is but still an issue. Ramshot magnum has proven to be a good choice. Same burn rate as Retumbo basically but with no powder bridging issues.
Happy with the one test rifle so its being offered as a chambering option form APS.
Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.
Can you build a 257 AX off a rem 700 270 chambering?? Only reason I ask is because I am already thinking of options to rebarrel this down the road. I like the idea of a 6.5-06AI, but I also like .257", and your 257 AX really intrigues me as I've always wanted a 257 STW, but matches that speed in a shorter action. If my .270 would accomodate that .300 Dakota case, I would almost rather go that route.