There has been a criminal lack of gun shooting on this site for quite awhile.  I apologize.  Last year in sunny Valdez we shot a propane tank, and have been wondering how to safely ignite the gas cloud ever since.  Last April, while waiting in rainy Valdez we discovered the answer.  Road Flares

P.S.   Our roommate Aaron showed us a far superior video on his digital camera of a propane tank they found washed up on a beach in Prince William Sound.  They chucked it into a bon fire and shot it with a shot gauge slug.  The tank above was shot with puny 7.62 SKS round.  The results of their ocean side antics were far more spectacular then that posted above.  Aaron, if you read this we would love a copy.