The Mark IIA was a modification of the army's Mark II anti-tank gun fitted with Molins auto-loading gear. Used by many MTBs in power operated mountings to give them a bigger "punch" when attacking barges and small vessels. It was also proposed to use the Mark II without the auto-loading gear as a wet mount for submarines but this never made it out of the prototype stage.
The Molins auto-loading gear carried seven rounds, one in the breech and six in the feed system. An additional twelve rounds were carried in ready racks on the naval mounting. The last round could not be fired, a precautionary measure to prevent the feed from running out of ammunition which would have necessitated manually working the breech mechanism.
Unlike the RAF version, this weapon allowed only semi-automatic firing.
These guns were of monobloc construction and actual bore length was 42.87 calibers. About 600 guns were produced with Molins gear.
|Designation||6-pdr / 7cwt QF Mark IIA|
|Ship Class Used On||MTBs|
|Date Of Design||1940 (naval version)|
|Date In Service||1941|
|Gun Weight||760 lbs. (345 kg)|
|Gun Length oa||101 in (2.564 m)|
|Bore Length||96.2 in (2.444 m)|
|Rifling Length||78.2 in (1.986 m)|
|Grooves||(24) 0.02 in deep x 0.22 in (0.51 mm x 5.59 mm)|
|Lands||0.0737 in (1.872 mm)|
|Twist||Uniform RH 1 in 30|
|Chamber Volume||100 in3 (1.693 dm3)|
|Rate Of Fire||40 rounds per minute cyclic
18 rounds per minute practical
|Weight of Complete Round||12.25 lbs. (5.56 kg)|
|Projectile Types and Weights||HE 1 : 6.0 lbs. (2.72 kg)|
Complete Round: up to 24.85 in (63.1 cm)
|Propellant Charge||1.31 lbs. (0.59 kg) NF 029|
|Muzzle Velocity||2,150 fps (655 mps) 2|
|Working Pressure||20.5 tons/in2 (3,230 kg/cm2)|
|Approximate Barrel Life||4,000 rounds|
|Ammunition stowage per gun||7 rounds in gun and feed mechanism
12 ready rounds on mount
|Weight||1.719 tons (1,747 kg)|
|Elevation||-10 / +12 degrees|
|Elevation Rate||Manually operated, only|
|Train Rate||40 degrees per second|
|Gun recoil||29 - 30 in (74 - 76 cm)|
This mounting appears to have been adapted from the twin 20 mm Oerlikon Mark V mountings.