Yes, I have shot it quite a few times. Shoots great. Back then, didn't know all the particulars (don't know much now about 1928s), but I had a friend that owned a heavy machine gun factory. Took it there and and all the quirks ironed out. Had to headspace, bought an original actuator, fixed the feed problem, etc. Makes sense now that it had all those problems. But they got it running well. Since I do living history WW2, used it in several reenactments. However, I don't reenact much anymore, so it has sat quietly in the gun safe. Even though it's a mongrel, I still can't part with it over sentimental reasons--which is rather silly, but there it is.
I'll keep on my search for a WH frame to match the receiver, keep the internal military parts to change over and just go from there i guess. Seems it will always be a parts gun, so shaving down the military frame is still on the table really.
Thanks for all the help folks!