The base guns these were built from were the Sterling Arms L2A3 submachine guns. It is evident that most of the actual props were castings taken from a master prop. We will discuss here the parts of the "master."
Sterling Arms Mk4/L2A3 Submachine Gun
Modifications to the guns involved the addition of six grips around the barrel. The exact identity of the grip material has yet to be determined, but recent revelations suggest hard black plastic T-track from old cupboards with sliding doors. Note: The row of holes on the underside of the gun had no grips as they would interfere with the folding stock. Also, the row of holes just above the folding stock on the left side of the gun received no grips, presumably this is because of the bayonet attachment stub that occupies the third hole from the front in this row.
On the rear of the gun 3 small, circular, detail pieces were added to the right side. On the left were added two detail pieces possibly rifle hammers. We are still researching these pieces...
Other modifications include the addition of a scope mount to the top of the gun in the form of approximately a 1cm wide by 1/16"-1/8" thick strip of metal bent down on the front end and attached straight into the rear sight in order to sit about a 1/4" above the gun. A stock M19 azimuth scope (see below), believed originally used on Sherman Tanks, was then attached to the mount. Also, small blocks were added just in front of and behind the scope. This mount and scope assembly was then, we assume, riveted to the body of the gun at either end of the mount.
M19 Telescope, 1942 M.H.R. Co. with bolts
The standard Sterling Mk4/L2A3 34-round magazine model L1A1 was used. These were manufactured by Sterling Engineering Co of Dagenham, Essex. The unique scalloped-edge design (seen below) distinquishes it from magazines made by other military contract manufacturers.
34-round Sterling L1A1 Magazine
Made by Sterling Engineering Co.
They were cut down considerably. The exact length varies between each prop (from 1/2 to 2/5 the original length). Both ends of the magazines were used. The blank firing versions used the feed end of the magazine which locks into the magazine well while non-firing models usually used the left over ends. On some of the guns there are magazines with the real bottom plate covering the exposed end. Others have replicated plates (no hole in the center) and some were just plugged with a piece of wood.
On non-firing versions of the prop like this one, the cocking handle was removed from the bolt and the ejector was removed. The ejector is located just behind the magazine well and is held in place by a retaining screw. The magazine catch had to be removed to release the ejector, but it was put back in after.
Sterling L2A3 Ejector and retaining screw
The bolt, where it shows through the oval cartridge ejection port on the right side of the gun was possibly covered with aluminum or chrome tape to help hide that these were castings of the guns.