The hard part is having magazines that function correctly.
The early guns seem to be very magazine specific, I have one magazine that works well in my early 1919 and most other magazines cause problems, they sit to low.
Attached is the magazine adjustment instructions for these, it says to file the rear rib down until they fit - I've found with mine that the ribs are too short on most later magazines to start with. To use those I would have to shorten the bottom of the slot in the rear magazine catch or add to the bottom of the rib on the magazine.
Also attached are pictures of three versions of the 5 shot magazine and the last picture shows a 7 shot that was modified for use in the bolt actions. The original design for the 7 shot had a sharp 90° corner on the rear of the follower to hold the action open after the last shot, for some reason this was eliminated for the bolt actions although some early magazines will still do this. The idea was to let the shooter know the magazine was empty and to stop dry firing.
