If it's military issue, the "rights" aren't an issue.

If I were making the M6 over...

1. Put an o-ring seal on the lid of the butt-stock ammo holder for better water-tightness.
2. Use a composite butt stock rather than stamped metal.

I also might want to find a source of .410 flares again...something in a 3" shell...surely the technology exists to make these...too bad the BATFE makes it so hard to make them,