Wrong catchLooks like it might be for a Marlin Camp 9
Strange heel catch slot
I've been googling heel catch firearmsYeah, I had noticed that also. I'm guessing "older" and "European" maybe, but other than that, I don't know. I am hoping that some knowledgeable guy here recognizes it!
I looked for the Hi Power first. Can't seem to find any samples to confirmHi Power mousetrap mag?
Not my pics, found one on ArmsList, copied the pic for reference. Might try Googling Bryco 59, see if any pics have angles you can reference.Can you rotate your mag and take a picture of it from the back?
I'm curious to see what else is in the boxes in your garage.I found about six of these in a box in my garage, been there untouched for probably 20+ years.