TM 9-1300-20 pages5-81 through 5-83 discuss the live version of this fuze and note it is for rotated ammunition 75mm through 280mm except 175mm.
5-56. Fuze, Mechanical Time and Superquick:
M520A1 (or M520)
a. General. This fuze (fig. 5-52) is a dualpurpose
fuze for use with rotated ammunition
caliber 75-mm through 280-mm, except 175-
mm. It has a 75-second timing mechanism, a
point detonator with superquick impact action,
and a booster which has a delay arming clockwork
mechanism for additional safety. Fuze
M520A1 is assembled with booster M125A1,
whereas fuze M520 uses booster M125.
assembly, point detonator assembly, lower
cap, body, and booster M125A1 (or M125).
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