Cartridge Case The M103 brass cartridge cases (fig. 7-6) are marked longitudinally or circumferentially with the caliber/case designation on the first line. The manufacturer symbol is on the second line. The interfix number, lot serial number, and year of manufacture are on the third line. Propellant All PGU-configured cartridges are loaded with ball spherical propellant WC 867. M52A3B1 Electric Primer The  electric  primer  is  used  in  all  current  PGU configurations. It consists of an open-ended brass cup that contains a brass button insulated from the cup by a plastic  liner.  The  firing  pin  of  the  gun  contacts  this button.  The  ignition  charge  (a  conductive  explosive mixture) is in contact with the other side of the button, and is retained by a paper disk and a metal support cup. The  electrically  initiated  primer  ignites  the  propellant charge. NOTE:    The    primer    explosive    element    is sensitive  to  electromagnetic  and  electrostatic energy. Projectiles All  projectiles  have  essentially  the  same  external configuration. The rotating band is copper alloy swaged into  a  circumferential  groove  near  the  aft  end  of  the steel body. PGU-27/B Target Practice (TP) The  PGU-27/B  projectile  consists  of  a  steel  body with a solid aluminum nosepiece swaged or crimped to the steel body. PGU-28/B Semi-Armor Piercing High Explosive Incendiary (SAPHEI) The  PGU-28/B  projectile  consists  of  a  steel  body with an internal cavity filled with a sponge Zirconium pallet, composition A-4 and RS 40 incendiary mix. The aluminum nose contains RS 41 incendiary mix and is swaged to the steel body. PGU-30/B Target Practice-Tracer (TP-T) The PGU-30/B consists of a steel body with an aft cavity containing the tracer pellet. The aluminum nose is swaged or crimped to the steel body. Tracer A tracer pellet is loaded into a cavity machined in the base of the TP-T projectile used in the assembling of the PGU-30/B cartridge. The heat and pressure of the propelling charge ignite the tracer pellet. The tracer is visible for approximately 3.2 seconds during projectile flight. PGU-27/B TARGET PRACTICE CARTRIDGE This  cartridge  (fig.  7-7)  has  no  explosive  filler  in the  projectile.  The  cartridge  is  used  in  practice  firing, for boresighting of weapons, and testing of new guns. The projectile shape and ballistic properties are similar to those of other PGU configuration ammunition. PGU configuration ammunition characteristics are shown in table 7-3. 7-7 Cartridge Approximate Unit Weight (grains) Total wt. (grains) (approx.) Designation Type M103 case M52A3B1 Electric primer Propellant Projectile PGU-27/B PGU-28/B PGU-30/B TP SAPHEI TP-T 1,855 1,855 1,855 22 22 22 585 585 585 1,550 1,580 1,554 3,900 3,900 3,900 Table 7-3.—PGU Configuration Ammunition Characteristics