[A Corpse]

I'm putting some serious hours into playing Pyro but the "Makin' Bacon" achievement, kill 50 heavies with the flamethrower, isn't progressing at all. It's still on 0. I've killed heavies, even solo, with just the flamethrowers, so I'm not sure if it's bugged or if I'm doing something wrong. Only thing I can think of is that I'm not using the normal flamethrower anymore, mostly the backburner. Does anyone see any progress on this one?

Also, how do pyros use their flamethrower as a melee weapon? I've seen it done but can't do it myself.