Can you tell me more about these "22" stamped mags. A friend came over last night to show me his recently acquired SMLE (from an aging FIL that purchased it from a Sask hardware store barrel full back in the 60's). It is a Lithgow, 1942, II* marked .303. (non # matching). The interesting thing to me, although it is a .303, the mag is stamped .22 the same as your picture shows. I have read that all trainer mags are hollow bodies just to collect empty brass however this one has a follower and spring in it. The follower is shaped different than any "military surplus" I have seen before, that being full length inside the mag body with a feed hump on one side. This follower has a large hole at one end (back end and I suppose it is to do the brass collection job) but at the front it has two ribs leading to the chamber mouth that would appear to be a track for rimfire ammo to be fed center of chamber. The owners of the gun claim to have used the mag to feed the .303 (holds ten shots) and it works flawlessly they say.
I own a BSA trainer that has the empty mag body that came with it but not sure if it is "original" to the gun. The folks that own the above rifle have offered to trade me the .22 marked mag for any old "surplus" mag that will fit their gun...on the hunt at the next avail. gun show.