you have been given a lot of good advice here
what I would ask is "have you had the rifle apart?"
then make a list and check the rifle/scope over and clean the motherfarker good and proper,
make sure the magazine box is floating, it has to have movement in it, and the middle screw is not tightened up just snug so it wont fall out!
by the way if you have had the rifle apart the rugers are supposed to be tightened to 95ft lbs at the angled king screw
I don't tighten my rugers to this amount and definitely would not on a plastic stock, I also would not tighten the rear screw as much as the front and would check for the action bending while being tightened up
then slowly start again with one brand of ammo only, making sure you are not the problem, shoot it prone with a rear bag, slowly
I have seen this because of : running in a factory barrel (can take up to 80 shots before it will settle down that I've seen if there are burrs in the bore),
a loose scope or action, mag box not fitted correctly in a ruger, middle bolt tightened up to much, oil between the action and a synthetic stock, a type of ammo the rifle does not like and ammo that is not concentric (roll your ammo on a pane of glass, glass table ect looking at the tip and see if it rolls or wobbles)
if your rifle shot well it should again, good luck with it all
“If you do not read the newspapers you are uninformed. If you do read the newspapers you are misinformed”. Mark Twain