Coastal Defence Guns

[Mike Cecil]

In short, the two terms encapsulate a number of different things:

BL = Breech Loading . These use a Bag Charge. eg M198 155mm; 5.5inch BL. and are loaded into the gun separately: projectile first, then the bag charge. The primer tube is also separate. Variation of propellant charge is possible at the gun by varying the number of Charge Bags that make up the Bag Charge (in most cases).

QF = Quick Firing where the means of obturation is by the rapid expansion of the cartridge case against the wall of the breech. There are three types of ammunition for QF guns:
(1) Fixed: these are fixed at the factory, and do not use Charge Bags (note: not a 'Bag Charge') Eg :18pdr QF, 20pdr QF Tank, 105mm Tank, etc
(2) semi-fixed: these arrive at the gun in two parts: cart case with charge bags and a projectile. They are mated once the correct number of charge bags have been removed (if any), and then loaded as a single cartridge, eg 105mm M101A1 (viz M2A2)
(3) separate: these arrive at the gun line separately, and once the correct number of charge bags are removed (if any) then the projectile is rammed into the chamber using the Rammer, then the cart case loaded, ie both components are loaded into the gun separately. eg 25-pdr QF.

Semi fixed and separate QF ammunition are a means to allow variations to the propellant charge at the gun.

QF and BL guns both load into the breech, but use a different means of obturation (simply, the means of preventing the propellant gases escaping to the rear).

Mike C