If that is a standard sched 40 1.5" barrel, you won't be shooting golfballs out of it...too small. You need SDR 21 1.5" for golfballs.
I like your use of the bell end on your chamber, ergonomic placement of the trigger and the effort you put into making your wiring neat. My only real complaint is the use of black tape to hold the trigger...it won't last and looks a tad ghetto.
You didn't say if your metering your propane or not. If you're just giving it a squirt and hoping for the best, a metering setup would be like night and day. I think you could even find a little fan to drop in there.
Overall, a decent cannon!...
