Ive had my mark II for about 11 years only thing not stock is I clearance the stock to float the barrel when I first got the rifle and put a scope on. Has always been a .75 or less MOA rifle at 50 yards. Has roughly 2500 rounds through it. Well yesterday just wasnt grouping very well was seeing 1 to 1.5 MOA @ 50yd. Then today my first 5 shots was .75. Then 1.5 and then 5.25 MOA. After every group was a walk to the target and a reload for cool down time. That was with Aguila super extra 40gr. So I tried some Federal automatch and it shot 1.5 to 4.5 MOA at 50yd. I cleaned the barrel and tried agian and same results starts with a .75 or less group and then goes crazy. Swapped scopes no change. Scope and rings and bases are tight. Action torque at 15in lbs. Went through Federal automatch, aguila super extra, winchester super x, federal champion, federal gold match, armscore. All had the same results groups 1.25 or less then out to 5+ even after the first group. Cleaned and not cleaned between groups. These are all done from a bench rest. Took all ammo and shot out of another rifle and it was consistent 1 MOA or less shooting 5 shots groups 4 times with just reloads for cool downs. Ive noticed a small ring at the end of my chamber before the rifling starts that Ive never noticed before today but only after it has been shot cant see it after running a patch. Even had my dad come out to the house and shoot it with the same issue. Has any one got and idea what it could be? PS yes its a youth model i actual prefer the shorter stock on the mark II.