I've had to fix several of these CVA drums. I bought the 7/16ths diameter drum from Dixie Gun Works with the 1/4x28 threads on both ends.........I then saw off the old CVA drum and drill and tap the hole thats left to 1/4 x 28 thread......Screw the drum in and line her up. You might have to file on the drum to get it to index up right. The CVA drum actually was unique in that it had larger threads that were long enough to screw through the Breechplug threads and help lock it all together. In other words you couldnt unscrew the Breechplug until you took out the drum as it screwed through the plug.......anyway the communication hole in whats left of the original drum is small enough to drill and tap ................Bob