Da Bomb: I recommend Moa Therma, though I didn't do it there. Syncopia is good too, but has more blind corners and sometimes the bomb spawns behind them.
Sharpshooter: There's no track, just count your shots and tap the button instead of holding it down. Done properly, you can get it with the very first Cannon clip you have. You can get it on Moa Therma while doing Da Bomb.