front rifle mounts

Do these work with M4 style rifles? Can they be flipped upside down?
They look like they are the same height as the old style ones that my truck has. The prop guns i have are too short, 16 inch barrel and stock fully extended. The stocks sit on not in the floor brackets and the barrel clamp bairly grabs the flash hider thanks

They made 2 different style mounts and brackets.
The newest is adjustable.
Give 86humv a pm he may still have a set.
BH

Or you can put a longer flash hider on.