Nerf Bazooka

Can a home-made Nerf gun be too big and powerful?

Possibly, but it will probably still be fun.
I'm pretty sure the biggest sticking point for my wife when she moved in with me was my rather impressive Nerf weapon collection. I am both proud and a little embarrassed to say that I had more than one fully automatic, battery-powered Nerf machine gun, including several that were still in the box. (The ones that were still in the box are currently up for sale on eBay through a broker, if you're shopping for the perfect gift for a favorite nephew, by the way.) And, I've always been given to extremes, especially when it comes to pushing that very thin line between "child-like" and "childish" behavior in my hobbies. So, naturally, when I came across someone who had made a Nerf bazooka, I had to share it.
I found Ryan and Dave via Gizmodo's article, but I highly recommend that you check out their R&D YouTube channel for all their other builds, too. There's not much on the making of the Nerf bazooka, but there's a lot of great video of them firing it. And more of their semi-deadly creations on their YouTube channel.

Either way, a great way to waste some time on a Friday instead of working!