For most modern centerfire cartridges, 300 yards isn't much of a stretch..........with practice!

IMHO, a .25-06 or .270would the way to go.They havemore than enough power to take anything in Texas at 300 yards (or better), shoot relatively flat,and nearly anybody can shoot one comfortably. My preference is a .25-06, mainly because I reload for itand use a lot of 75 gr. V-max's for coyote hunting. If I didn't do a lot of coyote hunting and planned on elk in the future, I might lean a little more to the .270. You can't go wrong with either.