Have used everything from the above Ford engine enamel which does work good........to cheap auto paint,just from a getting rid of it standpoint.And Hammertone is good stuff.
Really don't like spraybombs....BUT,they DO work.Cpl things 'round here that were done with a particular colour(it matches factory and is stupid cheap from chinamart)spraybomb,because I didn't want to mess with getting custom colour mixed.Been beating on these pcs pretty good and its held up way past what I'd've bet money on.
Tractor supply paint w/hardener,Naptha reduced...sprays like a dream with cheap gravity HVLP guns.Looks good....nice and thick,ain't expensive.You could play with hardener ratios if you gave a chit,using more or less to get a little softer finish.IOWs a vise would rather be a little softer(way longer drytime).
Gotta say though....really don't mess with primers.Well at least on castings........just get them spotlessly clean and start with topcoat.The trick to cleaning is loosening grime with whatever(acetone,laquer thinner,ect)and understanding the evaporation rate of said chemical.You don't want to just "redistribute" the dirt.This is what seperates different cleaners....its the open time.Also understanding how these chemicals soften any underlying paint....don't be sanding the grime into it.The dirt has to be removed.
It really depends on how you see the overall project......is it one of three on the planet?Or....a pce of industry that was made in the millions and its mission in life is to stop a hammer's blow?
Oh yeah....cold metal=Bad...use a heat gun and get the pce nice and warm.It helps with the flow-out.You can heat paint too....just be careful and not burn the shop down.BW