Regarding SN 5366i offered on the Greg Martin auction :
"Ghost" of a "P" on 5366i as Vern as noted...If a "P", then this was some M1906 Swiss Ordnance gun release from service-use by the Military :
File marks Vern mentions on 5366i :
I think the spacing of the 3 and the 6 on the front frame SN 5366i is a bit odd and not done well :
