This came up in a game a couple of weeks ago, and it isn't discussed in the rules so we made a decision between our group and this is how we ruled it.
The Delaque ganger is charging the Scummer who is on overwatch.
Normally this would be -2 to hit, -1 for firing on overwatch and another -1 for the target charging.
But the scummer is using a hand flamer that would auto hit, so would it automatically stop a charge?
We figured that this would be very overpowered and decided that you can overwatch with flamers, but in most cases this will only ever hit one model.
But if you fail to wound the model is not pinned as it normally would be if hit by any other shot. The assaulting model runs through the flames unscathed and gets into combat. Although if the model catches on fire it also doesn't get into combat.
Thats how we play it! Do you have any thoughts on it? I know its not something that would come up a great deal but I figured I would share it anyway.