I did get the combos to the highest I could, I don't believe I missed any shots.
I just don't think the random bullet damages & the timed reload offer much strategy?
Prepare for the secret of the game:
Each bullet is generated from an enemy on the screen, unless there are less than 7 onscreen, in which case it becomes random... therefore, if you plan exactly right, you'll never be shortchanged.
The way it works is that it randomly chooses an enemy that exists, and then rolls from whatever their hp is, to 6. So if there's a big slime, it'll be 4-6, or if there's a small slime, it'll be 2-6.
It was the most important game mechanic I designed for this game, because I knew that if I didn't find a solution, the game would be unplayable as it was originally intended.
That said, you can still get lucky and have multiple rolls that work for multiple enemies.
Also, not to brag, but I did Ace the challenge once to make sure it was possible to do.