Loose when the action is open or closed? If it's when open, it doesn't matter, but closed it should be tight. Although it's not as critical on the Huntsman as it is on a cartridge firearm, it's also not good. Close it with some force to see if it just needs some break-in time for the latch and shelf to get used to each other.
If it's very loose at all, I'd contact H&R and have it repaired/replaced unless you want to do it yourself, barrel fitting info is in the FAQs sticky, it may just need a pop can shim on the hinge.
Tim