The protagonists of both series become someone completely different when they fight... and on some other occasions. I don't think going into details will help this recommendation, but know this: those series do feel alike for some reason.
It's just a hunch, but something tells me you might like Zero In if you liked Dollgun. Maybe it has something to do with the relationship between the male and female lead. Anyway, just give it a go.
P.S. Zero In has more coherent story and way less ecchi.