Spud gun safety?

I just glued the barrel. but before glueing it i thought i'd try it out, so i put the barrel in he reducer, put some propane in (first spud gun! should i use hair spray for the beggining or i could start right off with propane??) and ignited it with no potato inside. It's my first so i didn't know what to expect; the bang scared the crap out of me! so i got frightened and before cramming a potato in, i thought i should ask: for the combustion chamber i used 2 pipes 10cm in diameter that are rated for 6, atm, one glued over the other and wd with reinforced tape. Could it blow up in my face??