A long time ago, there was a thread on this. Can't find the link, but from memory, Colt 1st and 3rd generation mags wouldn't work, 2nd generation would. The would hang up on the follower button (the thing you pull down to load the mag). The button sticks out to far to enter the mag-well.
Take this with a grain of salt, it was a long time ago.
Pop over to RFC, you might find the answer there.