When the Thompson was first introduced, one of its selling points was its ability to fire a .45 caliber shot shell. These were paper nosed cartridges developed by Remington-Peters, containing 120 pieces of number eight bird shot. Because the shot shells were slightly longer than standard .45 ACP, a special box magazine was provided. This same shot magazine was used for the M1923 with its longer Remington - Thompson.45 cartridge. There were three production versions of this magazine.

The first production shot magazine looks just like a first production Colt Blank Magazine except it is wider. Only a few of these magazines have ever been seen.

The second production shot magazine had the following stamped on to the magazine body:

For Shot Cartridges
Patented - Aug. 24, 1920
August 24, 1920 - Jan. II, 1921

It was soon discovered that if the magazine was fully loaded with twenty round of shot shell ammo, the first two rounds fired would jam. The paper nose for the shells were crushed by the strong spring tension. Thereafter a second production magazine was produced.

This magazine's markings were

Patented - Aug. 24, 1920 For 18 Shot Cartridges
August 24, 1920 -Jan. 11, 1921

These magazines were also shipped from the factory with the markings whited up to allow their unique markings to be seen. The 1922 Auto-Ordnance sales catalog describes them as follows: