is it possible to use aa guns on bomber hardpoints?

ive fiddled with guns settings on my bomber to try and mount AA guns, if i mount them my bomber plummets into the floor, so i tried using the standard guns but with flak rounds but they dont seem to be doing any damage but the effects are good, i used to think there was a mod to do this but ive looked everywhere and had no luck does anyone know of a mod to do this or could tell me how to mod it pls?