Interesting finds after shooting my 1900 AE

[Ron Wood]

Use a piece of masking tape on the rear of the frame just under the rear projection of the toggle, not the breechblock. The opening motion of the toggle is stopped by the little projection on the very end of the rear toggle link striking the frame. The masking tape test is a firing test. With the masking tape in that location three things can happen 1) if the mainspring is too strong there will be little or no impression on the masking tape; 2) if the mainspring is about right there will be a light impression on the masking tape; 3) if the mainspring is too weak there will be a strong impression on the tape and sometimes it is even cut.