I have only seen one. I was told the chamber insert was made from a Mosin–Nagant 91/30 barrel stub. (Some of 91/30’s were imported as parts kits. They had the barrels cut up, but the chambers were usually intact.) The man who had didn’t have any more information. I couldn’t see any sign of threads. I think the threads had been turned off and the insert was pressed in, like a PSL barrel is pressed into the trunnion. There was no sigh of it being pinned though.