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The BSA machine carbine was a British submachine gun designed by Birmingham Small Arms. Intended to replace the British Army's Sten gun, it was fed from a side-inserted folding box magazine and had an unusual cocking "sleeve" that functioned in a pump-action fashion.


The BSA Mk.I in cocking configuration.

The BSA Mk.I in folded configuration.

This weapon was designed by Birmingham Small Arms in the mid-1940s. The first prototype, the Mk.I, was unveiled in 1945, where it was demonstrated at RSAF Enfield. It fired at 530 rounds per minute and performed impressively, despite being slightly heavy.

It was not until 1947 that trials for the weapon were arranged, by which time it had been improved as the Mk.II. It competed against the MCEM-3 in June, and was deemed favourable due to its stability. The design was modified later that year and it was given a curved 30-round magazine and two alternative methods of cocking. This improved model once again trialed against the MCEM-3 and several other contenders; the Australian Kokoda No.1, the Patchett gun, and the STEN gun. The trials were held at Pendine, starting on the 8th of September and ending on the 16th.

The second prototype, the Mk.II, designed in 1947.

The BSA Mk.II got the best report of all the competitors and an order of 100 models was placed for troop trials. The costs of production proved so high that the order was reduced to a mere 6 models. The 6 weapons were tested and returned to BSA for improvements for the trigger mechanism, and adding bayonet fittings was now mandatory since general staff specifications now required every submachine gun to be able to fit a bayonet. This proved inconvenient, since the unique cocking sleeve of the BSA Mk.II could not accept a bayonet. The whole cocking sleeve had to be redesigned. These modifications proved to be detrimental to the design, and in 1951 the new Mk.III model was tested against two different models of the Patchett gun, where it was discovered that the new redesigned cocking sleeve of the BSA Mk.III was fragile, stiff and awkward to strip.

The third and final prototype, designed in 1950.

In May 1951, the BSA Mk.III was trialed against the Patchett gun, the Australian MCEM-1, and the Madsen Model 50. The BSA Mk.III's cocking sleeve was still stiff and would not function in sandy conditions. It was decided that even if modified, the BSA Mk.III would be no better than the Patchett gun, and in 1952 the BSA Mk.III was rejected outright. BSA felt that the sudden changes of specifications had negatively impacted their design and was the reason for the weapon's failure.


The BSA machine carbine was a unique submachine gun design that incorporated an odd cocking mechanism. The fore-end was comprised of a plastic "sleeve" which was pumped forwards in order to cock the weapon. Initial models had straight magazines that were inserted into the side of the weapon, much like the Sten. The magazine well could fold back so the magazine did not stick out, but this was only to ease carrying and the weapon could not be fired in this configuration. It also had a folding wire stock. The large fire selector was on the left side of the pistol grip.



  • An Illustrated Guide to Rifles and Sub-machine Guns, Salamander Books 1981, ISBN 0861010779, English, 164 Pages
  • Modern Rifles & Sub-Machine Guns. Hardback 160 pages, published 1992