Magazine has nothing to do with fitting jn the box, the base plate is the 100% cause of that.
9+1 means 9 in the mag, one in the chamber.
Obviously, if your shooting ipsc don't waste time or money on 9round mags.
Depending on your knowledge of 1911, the magazine is just as important as the extractor for reliable function.
Proper height and feedlip dimension all produce magic or hell.
Before you go spending 350$ on 5 or 6 new mags, experiment with other poeple's mags first.
What works for one 1911, probably will not work for another, but there is always a proper match.
Wilson
Tripp
Brownells
Are the most common i see.
Tripp tends to be a winner. But i know alot of players that swear by them, then are clearing jams. (Slide ride, mag issue? I tend to not ask)
I have always used wilson Emt v2 (metal followers) they have been flawless in an sti trojan and multiple springfield