NEWS | Feb. 4, 2020

M120/M120A1 Mortar: Firing Pin Alignment Doesn’t Have To Be Exact

 M120/M120A1 Mortar Firing Pin Alignment: It Doesn’t Have To Be Exact

TMs 9-1000-202-14, 9-1015-250-10, 9-1015-250-23&P, and 9-1015-256-13&P for the M298 tube used on M120/A1 mortars say the barrel’s white line should align with the white line for the firing pin on the breech (or base) cap.
Correct and incorrect firing pin alignment.
Don't needlessly deadline mortars; as long as lines overlap even slightly, mortar is ok to fire
If the white lines have some overlap, the cannon is OK to fire as long as:
  • There is no evidence of gas leaks, metal discoloration or excessive erosion around the area where the barrel and breech cap meet.
  • The breech cap is free of cracks, dents, bulges or other unusual wear.  
  • The firing pin is fully accessible for removal for misfire procedures while the mortar (cannon, baseplate and bipod) is emplaced.
If the white lines are wearing off, they can be touched up. The lines should be 0.39 inch wide. Of course, don’t make the lines wider to correct a misalignment.
Mortar fire control system (MFCS) and mortar components will work fine with the slight misalignment of the lines.
The TMs will be revised to clarify the alignment procedure. For more information, see TACOM Maintenance Advisory Message MA18-035: