I have 3 cartridges in my collection that are old rimfires. They appear to be the same as a 38S&W centerfire, except for the primer system of course. (Attempts to photo and post have met with utter failure.) That is, same case length, diameter, etc but the bullet is a soft lead with groves in it (3 under the case, 1 exposed). The case seems to be copper, not brass. They are very dark, having been poorly stored and exposed to unfriendly conditions.
Are these something I should keep or trade off? Metallic rimfire cartridges are really not my area of interest.