I use a hi/low heat gun from Wagner. I vary the time over the heat according to the size of the jig head. I also haven't scortched a jig since I switched away from a propane torch to the heat gun.
Even on hi, the heat gun takes 8-10 seconds to heat my 1/4 and 3/8 oz football jigs to the temp I like, so the powder melts and glosses.
Maybe higher powered guns heat faster, but this works for me.
I read here that people use their toaster ovens to preheat a lot of jig heads before they powdercoat, but I can't manage to get stuff out of a hot toaster oven without burning myself or dropping the jigs, or both, so I don't do it that way.