zlacker

Looks like a completely stock S&W M&P 15 Sport II, 16” barrel, GI style mag, collapsible stock, plus a cheap airsoft optic.

M&P 15 is a complete knockoff of US military M4/M4A1 carbine, except barrel is longer and has no full auto function to comply with regulations.

Way too boring configuration to build from parts or build out of an 80% blank, and also probably not an airsoft.

Disclaimer: I’m an airsofter outside US at best in the context

>>numpad+(OP)
You got this backwards, an M4 is actually a knock off of the AR-15. That is to say the AR-15 came before both the M16 and the M4 and both of those guns were built from the AR-15.

>>tekkni+nm2
I mean that pictured gun is an M4gery isn’t it

>>numpad+jt2
Sure? If you mean it's probably a 16" with a carbine-length gas system, tube-like handguard that probably isn't floated, and a carbine stock, that looks about right.

It's kind of an ill-defined term, and doesn't really mean that it was purchased whole. It could easily be a stripped lower + lpk + complete upper, or complete lower + complete upper. Either of those sidesteps the 10 day waiting period, and it's about the same price - you can get a lower+lpk with buffer tube and halfway-decent buttstock for something like $120, or you can buy a complete lower for about that same price.

Assuming you just buy a stripped lower and not an 80% lower, assembling requires minimal tooling - a couple roll pin punches, a hammer, some pliers, a hex wrench, and maybe another wrench. A vise grip makes it easier but isn't strictly speaking required. Takes like an hour or two even if you have no idea wtf you're doing.

That said, I agree it's probably more likely they bought it whole, or bought a lower+upper and just slapped it together (which takes 5 seconds and zero tools).