Hi,
Having read the initial post, and replies, I would like to add to the discussion. I agree with trying other brands/bullet weights. One to avoid is Winchester XPert, a bulk-pack loading that is not worth the money. I made the mistake of buying a whole case and was giving the stuff away to people when I found out how bad it was. They reported back to me the same results I was getting. Three Ruger .22 pistols, a 10/22 and Henry Lever action told quite a tale of misfires and weak rounds with the XPert ammunition.
On your Ruger 10/22 and getting "shotgun patterns," did you check the barrel retaining nuts? I found mine to be loose after a shooting session. Also, you might consider a replacement barrel unless the postal match doesn't permit such.
My personal choices run towards CCI Mini-Mags, and am especially happy when the gun shoots it better than I can hold.