The barrel is simple enough:a threaded bit of steel tubing that screws into the bolt and epoxied in place.
Screws and epoxy are not going to pass BATF scrutiny... Welds or destroyed permanently, not epoxy and screws, that is readily convertible...
There are threads here that discuss in detail what possible steps should be taken, if you search...
Now take the guts out of the fire control group and just hook a spring up to the trigger so it'll pop back if you squeeze it (plus the tube I describe above will have no provisions to let any of the fire control parts fit)
The sterling will fire full auto without the trigger assembly in place just fine, in fact the trigger assembly is the only thing that prevents it from emptying the clip, in short yanking out the trigger mechanism has not effect on the ability to fire...
FYI the tube is the receiver if you make a tube you just made a machine gun unless it's altered in a permanent fashion to no longer accept the full auto parts, if it accepts legal semi auto parts you need to fill out the forms and register it...
If you want to disable the rebuild and keep non-gun status here are the primary steps that should be taken...
1. Breech end of barrel should be plugged and welded shut or machined out so it will no longer accept a bullet...
2. Barrel itself should be plugged and said plug should be welded in place...
3. Barrel should be welded to receiver so it can't be swapped out...
4. Bolt if used should be destroyed, I suggest machining the business end flat... Or use a fake bolt...
5. End cap of receiver should be welded on as to prevent removal of fake bolt or barrel, and/or a plug should be welded welded into the back end of the receiver to prevent fake/destroyed bolt removal...
Some additional steps I would suggest
1. Destroy trigger group
2. Do not cut out the portion of the receiver where the clip would fit in, the E11 already uses a modified clip so just trim the lips off and let it bump up to a solid receiver body vs actually allowing a bullet to potentially chamber...
3. Weld a plug behind the barrel, if you machine the front surface of the bolt flat it will still seat properly against the plug...
Receiver-wonderful ATF regs on this but where there's a will there is a way...
Yeah and better safe then sorry when you potentially face federal felonies and prison time over a laser blaster toy...
There is a way but solder, screws and epoxy are not it... Real welds and destroying the parts is... And neither is just tack welding a few parts in place like they do in many European countries, that won't pass the BATF scrutiny...
The only 'official' way to know if your plans and what you intend to do to make it a non-gun is to detail them and send them to the BATF for approval... If they sign off you should be safe, although they do have a history of changing their minds...
To repeat what Darkside72 said, I believe he has been there and done this many times if my memory serves me right...
It's illegal to manufacture a whole sterling receiver or own one unless it's a semi-auto.
UNLESS the receiver is compromised itself so that it is rendered non-readily convertible. Which means the barrel has to be rendered inoperable and irremovable. This is done by drilling/boring out the breach of the barrel so that a 9mm round can't seat and fusing/welding the barrel and receiver together from the outside.