Elephant guns are for amateurs. This home-brew .70-cal hand cannon will punch a hole clear through Godzilla.
This DIY rifle built by Youtuber JTCustomKnives uses a .700 lead cast bullet fitted inside a modified .50 BMG brass case. The rounds are so large, you can only craft six per pound of lead. The the 1132 grain of lead rockets out of the barrel at a stupendous 2300 fps and with enough force to penetrate a quarter inch of steel plating. That's roughly the equivalent of the McMillan Tac-50 .50 BMG sniper rifle—the one used to record the longest kill in history at over 2300 yards. It is a single-shot rifle, using a shell holder action—opposed to a bolt-action—that has to be extracted after each firing so don't miss.
I'm not sure how legal this thing is but damn if I don't want to build one of my own. [The Firearm Blog via Geekologie]