AssasinNF those are all valid points. For that very purpose I paid extra for rare earth magnets, I have 2 stuck on the side and each one is rated at being able to pull a 6kg load. If you put the box on at the right place, it takes some muscle to pry off. If won't fall off if you run with it ...but your arms might from the weight.
I have thought about putting another box on the side to catch the darts but I think the sheer weight will then make it impracticable to take around. As such, for now this is a display item/stationary gun.
Sorry, in Australia our army surplus stores are called "Aussie Disposals", so yes you can pick one of these tracer boxes up from there. It is a 7.62mm tracer box and it fits the 50 dart belt very well.
Those are some strong magnets.
I built a 75-round box out of polycarb, and a belt catcher out of CPVC and a pillowcase. Needless to say, it's rediculously heavy, and won't spend alot of time off of the mount I built for it. It's now just a defense turret for CTF games, but it's pretty damn fun to shoot.
You don't have to make the belt catcher another box. You just need a bag or something, like I did. It's much lighter.
And I agree with Galaxy. That is a wicked paintjob.