Im not sure why DON VITO said that my suggestion would only work for non US people??? The Sterling MK6 semi auto kit I listed
IS CLOSED BOLT people...look closer. It has a firing pin/striker that is INSIDE the bolt assembly. This is just like on a Glock pistol, the firing pin floats in the slide but has its own spring. When the bolt is blown back, instead of it being held back by the sear (open bolt) the bolt continues back forward as the striker is held back by the sear (closed bolt) When the bolt gets all the way forward you have the striker fully compressed inside the bolt itself. When you drop the sear/pull trigger the striker is released and it runs forward, ignites the next round and the process repeats. The bolt is ALWAYS closed upon firing....
The sterling MK6 FCG is also SEMI AUTO ONLY. It has NO provision for a sear trip for full auto. Accordingly it would be perfect for using w/a STEN to make a semi conversion. I proposed to hide the sterling FCG inside a STEN MK2/3 FCG housing (or sheetmetal cut to the same shape) and use a pull rod from the sterling trigger to the STEN trigger to keep the aesthetics as close to original as is practical. The only deviation would be the rotating safety. You could remove it and retain the original sten selector as a safety instead to block the STEN master trigger (since the original STEN sear/etc would be gone...)
You also gotta remember that the Sterling MK6 carbine was legally sold here until the 94 AWB. It is again legal. You could buy a $200 IMA sterling kit and the above bolt/FCG and buil a semi-auto Sterling for a reasonable price (much nicer carbine than a STEN, and can use STEN or Sterling magazines). OR use the parts in a STEN, as I suggested.... Good luck and stay safe