I vote pellet gun as well. It appears the ejection port is just a really shallow indentation, not an actual one. If the chamber was that thick, that means the slide would be like .060” thick...
"...muzzle projects past the slide..." Does on a Berretta 92 too.
A Beeman P17 it ain't. https://www.pyramydair.com/s/m/Beeman_P17/614
A very WHAG says long slide Glock. Hard to tell with the crappy lighting.
I agree with the bb/pellet gun or toy assessment. That black dot an inch behind the muzzle is probably a recessed screw hole fixing 2 plastic halves together.