Here you have someone expending a great deal of time to shoot a lego brick four feet. But this kid actually built a Lego repeating rifle out of, of course, Legos. This one is a model of the British Accuracy International L96A1. (Link is to the real, not plastic block, version). The same guy has several more versions out there. Sometimes you just know your kid is a future mechanical engineer.
Supposedly, there is a link there that lets you download instructions. Alas, it hits you with spams and then doesn’t work, so don’t go there. But it’s OK to look at the rest of his Lego guns on YouTube — we think.