Forge gunning is definitely one of my favorite things to do in game. It was extremely frustrating getting used to how they work and from time to time I still get upset by lining up the perfect shot and seeing it go as far in the opposite direction as possible. One thing to keep in mind is the splash damage is really significant and in the top end forge guns you can kill lightly armored targets with the splash damage alone. Also assault forge guns fire off two rounds "relatively" quickly, so even if neither hit is spot on you are getting them with the splash.

One of my favorite forge gunning moments happened this past weekend when I killed a few people and then a heavy and his logipet came around a corner. One shot to the heavy's chest and he was gone. The logi took a moment to realize that his heavy had been vaporized and his repper wasn't going to bring him back. His delayed reactions proved his demise as a second forge round went through his chest as well.

You don't get the forge gunner every time though, sometimes the forge gunner gets you.