HISTORY OF THE BOX
Improving The Old XX Box
Under the fateful date of December 6, 194 1, the Armoured Force
Board at Fort Knox, Kentucky issued a report of a magazine trial
of Thompson magazines, excerpted as follows:
Magazine, 30 & 40 Round for Thompson Submachine Gun .....
To test the 30 and 40 round magazines as possible substitutes for
the 20 round slip and 50 round drum magazine.
A total of 2,000 rounds were fired using the 30 and 40 round
magazines. Both types functioned very well from a mechanical
The 40 round magazines consisted of two (2) 20 round clip
magazines welded together front to front with a 7/8 inch offset on
the ends so that the end of each clip can be inserted in the gun.
The 30 round magazine is similar to the regular 20 round clip
except that it is 2 3/8 inches longer.
The 40 round experimental magazine does not appear to offer any
great advantages ..... in that after 20 rounds are fired, it is
necessary to remove and reinsert the magazine to fire the 20
rounds. The time required for this operation was from five (5) to
eight (8) seconds. A definite disadvantage of the 40 round clip is
that when firing from a prone position, the open end of one
portion of the clip has a tendency to gather dust and sand in it
while firing the opposite side of the clip. The 30 round magazine
offers the advantage of 50% more firepower before changing the
clip over either the regular 20 round or the experimental 40 round
magazine. Either type, however, is superior to the 50 round drum.
The Armoured Force Board recommends that the 30 round magazine
be substituted for the present 20 round clips and 50 round drums
for the Thompson Submachine Gun for use in the Armoured Force.
A close up look at the existing examples of the prototype
thirty-round magazine shows that two Crosby twenty round magazines
were used. The top of one magazine was cut off and welded to the
bottom of the second magazine. This adds 2 3/8 inches to the
length of the body. A longer follower spring was added to feed the
ammunition. The magazine also featured enlarged and numbered shell
counting drain holes in the side. However, these were not put into
production, due to the fear of dirt infiltration in the magazine.