Got pics of the bottom and follower? It doesn't look like an ACE mag from here...
Regards, Jim
It's pre Ace
Do you have the kit to accompany? How about some closer and maybe detailed pics? Markings?
Regards, Jim
The .22 mag could also be for a Colt Service Model Ace (SM serial prefix) which were ordered by the military beginning in about 1935. They are originally blue with a matching-numbered slide and many were parkerized when rebuilt. With either finish, these are expensive pistols and hard to find. If so, it's a scarce mag. Those I've had have had the diamond with "Ace" inside on the base and were blued.