Definitely an interesting concept for a game. I really like the core idea here of "rolling" for the amount of ammo in your clip.
That being said, what you can do with the ammo felt a little lack luster. It felt quite difficult to kill a single enemy, even on a "high roll" of 6 in the clip. I think the gunplay could have felt better if you made the bullets do more damage, or have some meaty knockback to them to fend off the incoming waves of enemies.
It's certainly a solid foundation and a neat entry. Thanks for sharing :)