Good way to burn your barrell out. Pretty cool show a while back on Mythbusters. They were trying to ignite a gas tank using tracer rounds. They were shooting military tracers in 5.56. They were just punching holes at 100 yars and getting nothing out of it. Finally, the tank was mostly empty and they moved back a bit. Found that the fumes ignited much easier than the raw fuel and the increased distance gave the rounds extra time to ignite and heat up. Kind of interesting.