If you are using factory ammo take the FPS number right off the box, and use that.
I can 1000% tell you this is horrible advice. Most factory loads overstate velocities by a lot more than you'd ever think. Also most factory loads are tested in 24-26" barrels ro show higher velo's but most hunting rifle barrels are 20-22". Find a chronograph or shoot a true drop test and do the math to get the velocity. Won't matter much likely out to 300 but if you stretch a rifles legs much you'll definitely see it then
