I don't have a G2 but have had Contenders for more years than I care to remember. It all happens on a Contender due to how the locking lugs engage. If the pin is sloppy, it could make a difference but before offering advice on the pin issue, it's important to know just how sloppy it is. Wrap the pin once with celophane or masking tape and see if it fits in the barrel lug. This could firm things up for you to troubleshoot better. again, without knowing how loose the pin is, I could be recomending things that will never work.
Second, use some crayon or lipstick and mark the lugs top, botton and face. Don't slop it on, coat the lugs as evenly as possible and attempt to close the barrel in the action. The crayon or lipstick will show areas of poor alignment with the cavity in the frame the lugs mate with.
Thirdly, what are step lugs? You mean two piece? That could be your problem too. The solid one piece locking lugs are more reliable then the split two piece lugs. Don't go grinding on your lugs before you're absolutely sure that they're the problem. I have never found a barrel that needed to have the lugs ground down. Changed to one piece, yes. Hope this helps.