My gun club has an upcoming long range match...20 shots in 30 minutes at 450 yards. Not long range to many of you, but it is to me. I am new to this. I own an 5.56 ar15 and a .300 wsm Winchester m70. I know the .300 would be the better choice ballistically, but I'm not sure I can shoulder 20 rounds like that, in my little experience with the rifle. Any tips...would a shooter's shoulder pad do the trick? Any other input? Thanks