The 3 barrels pictured are, from the top:
8" stainless in 7.62 x 25
7-3/4" (issue length) in 9 mm Luger
8" Bull in 9 x 23 Largo
Due to the taper of the case. the 7.62 x 25 requires a modified PPSh 41 magazine to feed properly.
The 7.62 x 25 will fit in the MP 28 II magazine but the straight body of the magazine causes feed jams
inside the magazine.
The 9 x 23 Largo barrel works great using MP 28 II "Schmeisser" magazines. These magazines fit
the Sten magazine housing simply because the British copied the MP 28 II when they designed the Lanchester.
The Sten design used the Lanchester magazine which was subsequently shortened from 50 rounds to 32 rounds.