cartridge. You can tell the difference between the M254 and live ammunition by its appearance and by the feel of     its     nylon     composition.     M50     configuration characteristics are shown in table 7-1. M54A1 HIGH-PRESSURE TEST CARTRIDGE The M54A1 cartridge is used only for proof firing of the gun at the place of manufacture. The projectile is made from a solid steel bar. It has a standard rotating band. The M103 or M103B1 cartridge case is used with the M52A3B1 electric primer. M55A2 TARGET PRACTICE CARTRIDGE The M55A2 cartridge has no explosive filler in the projectile. The solid nose is made of aluminum alloy. The projectile shape and ballistic properties are similar to those of the other M50-configured ammunition. The cartridge   is   used   for   practice   firing,   boresighting weapons,  and  testing  new  guns.  The  M103  cartridge case   and   M52A3B1   electric   primer   make   up   this cartridge. M56A3 HIGH-EXPLOSIVE INCENDIARY CARTRIDGE The  M56A3  or  M56A4  projectile  is  used  in  the M56A3  cartridge.  The  projectile  is  loaded  with  an incendiary   and   explosive   composition,   giving   the combined effect of the blast of a high-explosive charge plus a fire-starting ability. Both  the  M56A3  and  M56A4  are  loaded  with aluminized  composition  A-4.  The  major  difference between   the   projectiles   is   their   construction.   The M56A3 has a baseplate to prevent ignition of the HEI charge by the propellant. The M56A4 does not have the baseplate, and it has approximately 10 more grains of A-4.  Both  cartridges  use  the  M103  case,  M52A3B1 electric primer, and the M505A3 PD fuze. M220 TARGET PRACTICE-TRACER CARTRIDGE The   M221   projectile   is   used   with   the   M220 cartridge. The M221 projectile is similar to the M55A2 7-3 Cartridge Approximate Unit Weight (grains) Total wt. (grains) (approx.) Designation Type M103 case M52A3B1 Electric primer Propellant Projectile Remarks M51A1B1/ M51A2 M54A1 M55A2 M56A3 M220 M242 M254 Dummy HPT TP HEI TP-T HEI-T Dummy 1,775 1,855 1,855 1,855 1,855 1,855 n/a None 22 22 22 22 22 None 635 (inert) 590 590 590 590 590 None 1,520 1,965 1,521 1,565 1,470 1,535 n/a 3,850 (min) 4,392 3,935 3,965 3,935 3,865 4,005 M103A1 Steel case M505A3 fuze required M505A3 fuze required Plastic Table 7-1.—M50 Configuration Ammunition Characteristics