I have a 20 gauge pump made by them(Union Fire Arms) which is only marked with the words "flussstahl-Krupp-Essen-H77" on the barrel and "Patent applied for" on the left side of the receiver. Underside of the action is "M60" "339" "3". Krupp is of course the steel company who made the barrel. 339 is the serial number. I have a second partial gun for spare parts and an extra shorter barrel. Same markings except the serial number which is 251. Interesting thing is that both guns have a solid rib.
The gun is very hard to pump because it uses a striker firing pin instead of a hammer. You get no mechanical advantage when you cock the gun. So the last half inch rearward travel takes 90% of the effort. You can see why the design failed the first time you try to pump the gun. Shooting doubles at skeet is very difficult due the the effort required to pump the action. You need to drop the gun off the shoulder to work the action.
