All those big boresyou mentioned are contained powder loads encased in a cartridge. When I speak about liabilities, I'm entertaining the thoughts of shooter/loader errors when loading smokeless powder in an uncased barrel -- such as the most common mistake -- that being double-loading of either the powder or bullet. When barrel blow-ups occur, the shooter will generally deny double-loading & proof that he/she did is sometimes never found. That's why the liability issue is a big concern to any ML company.

H & R has been in the same barrel-swapping game much longer. Have they ever introduced smokeless ML barrels in their interchangeable system??? If not, then something is going on that's either stopping this option - or delaying it. When this happens, it's mostly insurance-related versus poor product development.