That's a Mitchell 50 round teardrop drum. I had one when I was a kid and it worked fine for a while but later on became problematic and totally unreliable. I relegated it to my pile of junk mags to include old RamLine 30 round single stack magazines (that were reliable when new but with use over the years, became problems as well) and both the Ramline 30 and 50 round double stack magazines. But reading this post, I got nostalgic for the days of my youth back in the 80's, dug that old Mitchell drum out and decided to see if better ammo would work. When I was a kid, we used Thunderbolts and whatever cheap ammo we could get for blasting gophers and I began to think that this may have been what caused the thing to be unreliable so I loaded it with 50 rounds of CCI Stingers and went outside to see if it would work. Nope, You MIGHT get off 2 rounds but generally it was a one-shot wonder. Might be that the belt took a set over the years as I don't remember it being "that" unreliable but yeah, back to the box of crappy magazines of my youth it shall return! I will be sticking with Ruger BX25 mags and if I want a 50 round magazine, I'll get the BX25-2 magazines. But thanks for the trip down mempry lane. :)