Wow, almost been a week before I found something notable to post here.
This is what you would call a 'frankengun', the name takes from Frankenstein, referring to the monster Professor Frankenstein made from parts of multiple humans. Anyway, like the name suggests, this gun is made of parts from multiple guns, notably the polymer and steel stock from a HK SL8, recoil spring from an FAL and bolt and barrel from the Sten.
Put together, you get this bad-ass piece of unique fire power, costing it's builder little more than $100 US in parts.
I would take a guess that the builder is in some way associated with the military by the hint of ACU clothing in the side of the first picture and the M18 smoke grenades. Anyway, I'm out.