At one point, over 50.
On one of my ships, that I decommissioned in 2001, the Torpedomen found a bunch of .45 components and magazines in the bottom of a locker when we were emptying all the equipment and lockers off the submarine. They had a TON of magazines.
This was a few years after we had converted over to the M9 and no longer carried the 1911's. Everything was going to be tossed into the dumpster, so they put the word out for anybody that wanted anything and then doled them out. I got a couple magazines, but they wouldn't give me any more "because other people might want some".
After a couple days with nobody else coming to them, I ended up with well over 50 magazines.
I took them all apart, cleaned them all up nice, romoving any rust and oiling them up afterwards to protect them.
Tested each one in my colt 1991A1 and never had a single problem. (That's a lot of ammunition, by the way.)
I stored them away, nice and preserved, arranged from nicest condition to worst condition. Then, any time I ran across someone with a .45 who only had one magazine, I'd give 'em a couple.
In fact, the last person I gave some to was a THR member. Bugger sent me money for S&H, but I would have been perfectly happy just knowing they had a good home. Postage ain't that expensive! But in true camaraderie amongst gun owners, it was a nice gesture.
Counting the ones with my pistol, I have 9 total now...which means I could still give away two more while keeping my personal minimum of 7 magazines.
Seven...because 7 X 7 with a round in the chamber is a full box of 50, a nice convenient number when preparing to go to the range.