Sorry mate but this video does not prove that it works and I'm sure that it does not work.
The video skips and jumps about so you could of simply only shown when you got a good gun. In the video you didnt always get a "good gun", most people would not class the BAR as a good gud.
Also if people say this works 8/10 times or anything but 100% of the time then it is not truely a "good gun glitch"... I could buy a gun and jump in a cirlce while singing and scratching my nuts and 8/10 or even 9/10 times I could get a "good gun" in a game... because it is random.
I dont mean to judge but from all my knowledge of games, gaming and programming it is not possible to effect the box with any out side action (jumping,running, crawling etc). The only truely 100% "good gun" glitch was to open the box one the first map when the ? was gold but that has been solved.
I hope this is 100% but I am highly doubtful.