At one time, Navy Arms Co. in Ridgefield, NJ imported and sold the Greener shotgun on the Martini action. At the same time they offered the acion alone, and rifles built on these actions in .45-70 and .444 Marlin. In his book "More Single Shot Rifles", Frank de Haas describes and compares the shotgun action with a Martini-Enfield action. The shotgun action was heavier, but shorter than the Martini-Enfield, but the bolt in the shotgun action was longer. The sidewall thickness of the shotgun action was greater than that of the rifle action. de Haas considered the action strong enough for the .30-40 Krag, .303 British, .348 Winchester, .444 Marlin, .45-70 and other cartridges of that type.
Navy Arms said in its ads that the guns were proofed at 65,000psi, and that should make them adequate for any of the listed cartridges or another round of similar pressures.
I think that the way to distinguish the shotgun actions is by the small screw above and slightly forward of the screw above the front of the trigger guard bow. That screw was used to anchor a bolt that secured the rear of the forend on the shotguns. I belive that the one on gunbroker was built from a shotgun or one of the Navy Arms imported actions by the shape of the rear of the receiver and the presence of the screw mentioned above.
