I've killed them, so I don't have "too much trouble" per se, I just seem to find myself plinking away longer than on other craft.
Rangoon for example, I pulled in point blank behind a BREW that was intent on bombers. I'm in a 110C. I know my main hitting power is the MG/FF. I'm close, not missing any rounds, no convergence issues... I unload and have to sit there pounding him for 2x longer than I expected before he simply lost a wing.
Didn't go boom or anything, just lost a wing. I was hitting the fuselage area as well (must have been wing root damage) so I should have popped the pilot easily.
(EDIT: I'm not saying anything is wrong, just recounting how it seems to me -- just a perception and it could be placebo or based on outside factors)