The latter really helps set apart the players haphazardly shooting the barrel from the players haphazardly "shooting" the barrel. Lol, get it? XD
Opponents typically jump around to dodge Drake's Level 3. If you initiate Level 3 while near someone, it's best to jump with the opponent to make that first shot easy to land.
After that, it's mainly up to good timing. Keep trying to jump with your opponents and shoot during the peak of their jump (or near the peak if you're at a distance). That usually helps helps me out with that.