I went prarie dog hunting in Oklahoma and got addicted with one fix. I called Hart and he recommended a 6mm br with a 1 in 12 twist for 68 to 70 gr. bullets for ranges out to 500 yds or so. Then I got recommended to this site to read about the caliber. After reading everything I can find, I am wondering if my 1 in 12 barrel is going to shoot anything but a 68 to 70 gr bullet. Is shooting a heaver or lighter bullet going to actually hurt the barrel? Are any of you guys shooting a heaver or lighter bullet in your 1 in 12?