Thought I'd mention that some guns, like the UZI have a registered receiver versus registered bolt option. For them the registered receiver is much more flexible, 'cause you can change caliber from 9 mm to 45 or 22 without having to pay any more tax. RR caliber change kits are much cheaper, like in the $250 range instead of over $1700 for the various sized registered bolts.
My 2 cents worth.
