I'm a magazine black hole. In 50 years shooting I've yet to sell one mag I found worth anything, why, even in the Clinton drout I managed to grab 10 promag glock 17rounders that were TOTAL FREAKIN FLOPS. When I called Promag they said since they were in Kalifornia they could only ship me 10rd mags as replacement, OR, they could send me 20 1911 blued mags which I JUMPED on as I have literally thousands of 1911 mag rebuild kits I bought from a gunshop going out of business back when I had my FFL. These mags have been running as range mags since the 80s ban with nary a one malfunction, and I'd remember, all my mags are numbered with logs.
Sometimes I'm so freakin bad I buy mags that are at killer prices for guns I don't even own, I get em home, oil and clean em then vacuum seal em and put em away for when I do get the gun they fit. My best magazine haul? Gunshow at the Coliseum several years back, this was a walk in private seller who bought a table, he had two boxes full of Beretta GENUINE INOX mags for 10 each, I offered him 8 each cash if I bought em all, which I did, along with a Rossi lever action 454, a used 5906 and a used 586 4".