If you have the new M1A1 semi-auto from Auto Ordnance (which is nearly exact to the military version except for semi, barrel length and magazine catch), to use a real mag from WWII or after, you need to oval-out the mag catch hole in the magazine in the military version. A file or Dremel works fine. This done, they work just fine.
A little Dremel Work,
Okay ,I’m good, Thanks.
10 round sticks look goofy,
but I got a great deal years ago.
See you at The Range!