In reality, water (or liquid) is more heavier than the air, so water gives you more resistance than the air. Such as: Difference between walking on the road and walking in the water.
So guns in underwater should limit its effective ranges up to 10 meters.
I was actually thinking about this, I was thinking prehaps a speargun could be added for underwater combat (breaks leg, causes player afflicted to sink, alongside 76 base dmg?), alongside bows (which I think have slightly better ballistics underwater?) Being the primary ranged weapons under the seas.
Also grenades, increase there blast radius underwater, as there actually more lethal underwater aince the shockwave rupture creatures much more effectively.
An arrow launched from a compound bow is going to do nothing underwater. Friction is going to be far too much on the long, slender arrow and the wide, flat bow limbs. You’d be a bit better off outside the water shooting into it, or, better yet, just use a speargun.
A bullet launched underwater will be more effective, but not quite practical. At that point, actual underwater firearms will be your best bet. Those underwater firearms may also be better than a speargun. However, outside of water, underwater firearms become more inaccurate than typical firearms. Underwater pistols suffer the most, but are easier to maneuver with when actually underwater than an underwater rifle would be.
In a nutshell: neither would really do all that much, with most projectiles only travelling a few feet. Comparing the effectiveness of guns vs. bows, a bow has too much “going on.”