The 16 bore Husky I had, had the right barrel straight rifled and .705" (13bore) groove diameter and chambered exactly the same as the 16 bore smooth and choked left barrel. Thus brass cases in the right barrel, paper or plastic in the left. Both would 'take' 16 bore plastic hulls that I used. It had 2 5/8" chambers, not 2 1/2" and almost perfectly matched the length of standard 16 bore supposedly 2 3/4" Federal hulls.
That's an odd combination on that ML SxS, Ed. Interesting gun indeed - about .64 cal.