I agree that the crown is worth looking into (take a Q-tip and rub it lightly around the crown. It should'nt leave any hairs behind.), but it seems you're on the right track. Being pretty much a novice, I had issues with my .308 this fall (My first experience with Handis) as well. I wound up sending it back for a trans bar upgrade, which can definitely affect accuracy (it was free). It was an improvement for sure, but I still had to tinker with it (being somewhat anal on rifle accuracy). One biggie was that the previous owner had oiled the daylights out of the receiver latch and everything around it. I had spent weeks trying to get that stuff cleaned up! The folks at the repair center got that all clean & dry (they had better luck than I did), which helped.
Next thing I did was remove the forearm, lightly widen the lug hole with a rat-tail file (Lightly!!) until the forearm slipped on and off easily, then added the O-ring and snugged (not overtighten) the screw.
BLAMMO!!! It was shooting nice tight groups at 100 yds!
That's when you finally get that smile that won't go away!
I hope you get it figured out. Sounds like you might be sending it back to H&R to fix it.
Good luck!!