300 Hamm'r Cycling Problems

Bought a new Wilson .300 Hamm'r Upper and had problems with it cycling. One shot and it would "short stroke". Changed from Heavy to Standard weight Buffer same problem. Shooting a 125 gr bullet with 26.0gr of CFE Blk. Non adjustable gas block. Looks like I need to increase my powder charge or change powder? 16 inch barrel here.

Well you do have some headroom. I would ladder 26.5, 27, 27.5 and work my way up. If you get to the latter and the bolt doesn't lock back I'd contact B.W. and Co