Many rifles have been in my safe over the past 54 years, and I was able to shoot only one as a true half-incher. That was a box stock Ruger M77R 243 purchased new in about '82. I would lay empty 20 gauge shotshells on top of the hundred yard board and clean them off with one shot each without ever touching the board. The load was 100gr Sierras over Win 785 powder (forget the charge weight). I came close to that with my Winchester M70XTR Featherweight 270 shooting 130 Sierras over the same powder but could not quite break the 5/8" barrier. I cried when they discontinued W785.
