Can the HSB Ruso 410-44 fire the 44-40 caliber?

Answer 1

Yes - in fact, that is the .44 calibre cartridge it is intended for, the .44-40 shot cartridge, which uses either a paper or wood sabot to hold the shot. Most that I have seen are also capable of firing the .44 XL, which is a lengthened .44-40 with the shot inside of the brass, rather than using the sabot. While you can fit a 2-1/2" .410 shell in the HSB Ruso, it should not be fired - it's only chambered for the 2" shells. IIRC, the only 2" .410 shells are the high brass shells.

THIS SHOTGUN IS NOT DESIGNED NOR INTENDED TO USE MODERN .410 SHOTGUN SHELLS, AND SHOULD NOT BE USED FOR SUCH. The .410 used in the HSB Ruso (and other .410 shotguns of the period) was something of a predecessor to the modern .410.