Sniper + shotgun would works much better than crossbow if you want some spike damage action. Shotty without full-auto is good enough, although with that feat, it becomes devastatingly powerful, I think I managed to deal ~400 damage at Depot A before
Sniper build starts working in mid-game, after you get Dragunov, since it's usually quite rare to find Rapid Reload for your low AP sniper
Or if you don't wanna use shotgun, energy pistol + jkk like your original idea still works fine