Projectile, 155 mm: Illumination, M485, M485A1

composition and the main parachute. On the 155 mm Illumination M485 the base plug is secured to the body by shear pins only. This projectile is no longer produced but may be encountered in service. The 155 mm Illumination M485A1 has the base plug secured by shear pins and twist pins. The M485A1 is no longer produced but may be encountered in service. The 155 mm Illumination M485A2 has a revised canister assembly and the canister fins are perforated to decrease the rate of deceleration before the main parachute deploys; the 155 mm Illumination M485A2 is the standard US armed forces variant of the M485 series and is the only one now in production anywhere. In operation the nose-mounted time fuze functions at the preselected time and ignites the primary expulsion charge. The Propelling Charge M4A2 is a white bag charge using 5.897 kg of M1 propellant divided into a base charge and four increments for firing as Charges 3 to 7. The increments are tied together by four cloth straps. A 96.4 g clean-burning igniter charge in a red cloth bag is sewn to the rear of the base section and an M2 flash reducer pad is assembled in front of the base charge. The complete charge is 533 mm long. The Propelling Charge M4A1 is similar to the M4A2 but does not contain the M2 flash reducer pad (although this can be added if required) and the base igniter contains black powder. The Propelling Charge M4 is a white bag charge differing from the M4A1 as it consists of a base charge and two increments only for firing as Charges 5 to 7. The M2 flash reducer pad is used with this charge. The M3 and M4 series of charges are fired using the MK2A4 or M82 primer.