Algodoo

Kel-Tec SU-16B 5.56x45 mm (223 Remington) civilian/sport rifle.
To shoot:

1: Cock the weapon using cocking handle (mag is allready in).
2: Pull the trigger. (its semi-automatic but its very easy to make it full auto by deleting just 3 parts)
3: If the mag is empty, remove it just by pulling it out.

Warning - only bipod is retractable, buttstock isn't.
All spare mags are hidden in the buttstock, just like in real Kel-Tec.
In case of misfeeds or jamms just cock the weapon again.
Have Phun.