The springs in Sten gun magazines make them particularly difficult to load by hand, as explained in the user’s manual issued at the time:
Owing to the powerful spring it is not possible to fill it quickly by hand. A filler is, therefore, provided.
A number of different sten loaders were produced, the first of the two we will look at tonight, the Mk 2 is a metal box with a brass lever to depress the spring of the magazine:To give it it’s full title this is the ‘Filler, Magazine, 9mm Machine Carbine, Mk2’. The loader fits over the end of the magazine:The brass lever has a finger hole that allows the operator to move the lever up and down and feed the rounds into the magazine:This loader is marked E & Co +:A second and simpler loading tool is the Mk 4:Again this is officially known as ‘Filler, Magazine, 9mm Machine Carbine, Mk4’ and this clips onto the side of the magazine:The lever on the top helps depress the spring of the magazine to help with loading. The Sten Manual gives troops guidance on using the Mk 2 loading tool:
Place filler on the top of magazine and press home so that the filler catch engages in the recess on the side or back of the magazine.
Hold the magazine in one hand, groove in the magazine away from the body. Place the forefinger in the loop of the brass handle, thumb on the forward knuckle, second and third finger in the recesses provided.
Press the rear of the lever downwards, thus depressing the platform and leaving an opening into which rounds can be inserted. Take a convenient number of rounds in the other hand and insert one at a time, base first, under the claw of the filler.
As each round is inserted, raise the lever smartly and then press it down again. A full motion of the lever must be made in both directions, otherwise faulty filling may result. This action takes the round under the lips of the magazine and forces it down.
Ensure that the ammunition is kept clean and count the number of rounds; the number may also be observed through the holes in the rear of the magazine.
Remove filler by pressing the flat spring catch outwards and lifting off.