I'm not exactly sure what you mean, but it sounds as if you want to make a rifle from a Sten parts kit. To legally do that you'll need to do the following:
1. Make it a closed bolt gun. It cannot fire from the open bolt like the original Sten did. If it does, its legally the same as an unregistered macheinegun, even if it only fires one shot per pull of the trigger.
2. The barrel must be 16" or longer. You can make it with a barrel less than 16" but only if you register it as a SBR (short barreled rifle) on a BATFE Form 1 prior to making it and pay the $200 tax
3. The receiver tube must be sufficiently different from the original Sten receiver tube that it could not be re-assembled as a machinegun with a new parts kit.
