Explosive bullets.
No, seriously!
A spaceship hull will always be a multilayered construct, as a large part of its job is to keep those Meteor(tm)-brand hypervelocity bullets out there on the outside.
An explosive bullet that chews a neat 1-inch spherical hole in the inner layer of your hull will be an annoyance for the maintenance and repair crew.
The same 1-inch spherical hole in the enemy's body armor will seriously inconvenience him.
Note that the ammunition to be used relies on its explosive power, not on projectile velocity to do its damage. Also, so they can be used in both gravity and zero-g with equal success, you would want a self-propelled bullet, that fires with virtually zero recoil. Something like the Gyrojet.
Conceivably, you could even make the projectile smart enough to only detonate on hitting an appropriate target. Although I have no idea how to fit enough brains into a small projectile like that, there are military minds that can think around corners like that. With projectiles like Smart Bullets, that somewhat aim themselves to a laser-lit target. If you can make them smart enough to aim, you can make them smart enough to not explode if the impact target is invalid.