Long Frame Main Spring
 

Do all long frame models use a leaf spring?
Aldo35

No. Both the P.04 and the M1900/06 (which used coiled recoil springs) initially came in long frame models. The long frame is identified in the chamber area (between the locking lug of the receiver and the mounting point of the barrel.). The helical recoil spring was a characteristic of the "new model" which followed the original M1900.

In addition, all Swiss are long frame but after 1906 they have a coil mainspring.