In a pistol caliber, like 9mm, 5 inches of barrel will give you effective velocity. I'm not sure what porting it will do that's worthwhile. There are a lot of 9mm AR15s set up this way, and it looks like an intergral, but it's a muzzle can.
The host rifle, in the case of a Sterling would have to be an SBR, anyway...if it's not, your suppressor/barrel combo will have to be 16 inches (or the combination of the permanently affixed parts). Not so compact.
$400 in tax stamps, $1000 or more on custom suppressor, and it only works on one gun? If you're doing an L34A1/Mk.5 clone, I get it, but otherwise, not so much.
For a first time suppressor purchase, a .22 or pistol caliber muzzle can is a much better choice.