Arsenal SLR105 Para by Classic Army.
From stock this rifle is fitted with reinforced gears, piston, piston head, and oiless bushings. Pretty much everything on it is made in metal, and the foregrip is real wood (which I sanded down to paint it with a darker shade, originally it was too shiny and orange for my taste). It's as heavy as the real deal, and feels extremely sturdy.
Dirty bandages wrapped on by me, to make it look RAW.
Recently upgraded it with a 150% spring to increase distance of shots.