Unfortunately, I think you have diagnosed the problem correctly. The semi-autos (including the Garand, M1-A, and AR platforms) don't do well getting the bolt lugs fully rotated without a run-up to get some speed. They have trouble getting the extractor over the rim, otherwise. They are supposed to slam home.
Bumping the op-rod handle with your hand can work as long as you don't get a slam fire. It is done all the time, but you are safer letting it slam home. If you live alone in the cabin, I would put on hearing protection (in case of slam fire), then point it carefully in a safe direction and load it in the house and put the safety on before opening the door to go out on the porch. That will keep it quieter. If there are other people in the house, it just isn't safe.
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member