Have you clocked any .22 LR over your chrony to see if it is right? 2000 fps is WAY out of line for a 180 from a 12" barrel, you're right, that is rifle velocities. that powder charge seems about right as a max loading for a 180 grainer and 296/H110. Are you using a Shooting Chrony or another makers chronograph? An improperly set up chronograph can read fast too. If the sensors and the software are set up for say a 3' distance between and you are closer, the thing will read faster. 300 fps is a 15% error at the velocities you should be getting and what you are getting, something is wrong for sure. I don't think you could stuff enough 296 in a Max case to get that much more speed, not without being dileberately silly, and you don't strike me as that. Do some investigating before shooting anymore of that stuff. I don't think your load unsafe, you wouldn't be able to open that TC after such an overcharge, but you need to know why you are seeing that amount of velocity. Keep us posted.