no Sten mags fit in the Mk3 ammo pouches which are really common. Already got them sorted, they hold 6 mags each. its the backpack that I currently have problems with. There are 2 different sizes, small and large. The small one fits to the webbing with L straps which I have. The large one fits with L straps and blanket straps (which I don't have). I ordered a pack that was cheap hoping it was the small but its the large. Now its going to cost me a massive £6.50 to get the additional straps!