The rim recess on all four of my barrels is .075" to .078" deep, Rem and Starline brass have a .065" thick rim, so that makes about .010-.013" head space, although the ejector claw may keep it against the breech face so it's not an issue. I've had some no fires with Rem 9½ primers, but I attributed that to a bad batch of primers which I also experienced in a non-NEF firearm.
If it's an extractor barrel, the extractor may be allowing the rim to recess too far and would result in too much headspace, mine are all ejector barrels, so even tho there is too much headspace, the ejector claw holds the rim against the breech.
I've seen this issue on other barrels, where the barrel face wasn't even and the chamber was cut too deep, my fix was to flat file the barrel face so the cartridge rim was flush with the barrel face, then fit the barrel to a frame.
Other that creating a stop for the extractor claw, returning it to H&R is probably the best choice. If you do that, I'd call them and ask to talk to Gordon and get it straightened out, once and for all!

Tim