Great shootin on the 45-70.....the hmr rounds remind me of a trip the range one time shooting a 7mm mauser, all rounds were keyholing, come to find out there was a bush mid range at the edge of the range causing the bullets to upset before they hit the paper. It took a bunch of shootin before we figured it out, moved over one seat at the bench and it quit doing it! If that's not the case, I'd look at the muzzle and make sure the crown looks good, have never ever seen anyone write about a hmr keyholing. Are you sure it's a .17hmr barrel and not a 22mag barrel??? I have read of an NEF rifle being built with rifling in only part of the barrel recently, worth a look.
hope this helps,
Tim