You've left a lot of variables out of the equation. Your 280, may just be you: IE, trigger control and breathing. Is it a real light rifle? The 270 has definite problems. Is it bedded? Probably has uneven pressure on one side of the barrel as well...Properly bed that rifle and freefloat it and let us know how it shoots. Start shooting some 5 shot groups too, that will give a better representation of the ability of both shooter and rifle...