Sent in to TFB is another concept design for an ‘afternoon’ DIY submachine gun of particular crudeness and expediency. The majority of components are laminated together from readily available square section steel tubing, owing to its namesake. Apparently the only thing that cost anything was the STEN mag and compression spring. The model shown is a non-firing mock-up dummy for the purposes of demonstration only.

The trigger in this case is an absurdly simple arrangement consisting of a rectangle and square plate which pivot together.

Rather than being milled from a single piece, the bolt consists of a bar bolted into two lengths of square steel tubing.

The barrel collar is a near identical arrangement and includes an integrated feed ramp ground into it.

Full view:

For those interested in academic study, a detailed look at its construction can be seen here.