Given that we have only 2 piercing guns, we need to make them balance.
I think what we want is this:
Let's start by lowering piercing multiplier to armor by around 30%. Increase it by 15% on hull health instead. Hull goes down way too fast currently. Ships behave like fighters, not warships.
Mercury:
long range, able to destroy armor easily. At medium ranges, able to destroy components easily.
Short range should be useless
Gatling:
Should be able to be much stronger than mercury if you can get in its range. Already can't hit at long range.
For this i propose:
Gatling maybe should get increased rate of fire the more you keep firing, but but as rate of fire increases, gun turn radius should decrease. (and jitter should increase, but you said you can't do that right now)
Fire speed should be around 50% of what it is now for the first shots, up to 200% fire rate (and -60% turn rate) after a few seconds of fire if possible.
I think gatling should be really accurate for the first 10 shots or so, but you said you can't do that right now, so you have jitter. Still, it has TOO MUCH jitter in 1.3
Mercury, i would add a potent screen shake to zoomed view whenever you are hit with high-damaging projectiles (other mercuries, lumberjacks), and medium shake when the ship is going faster than speed 1.
Mercury damage is fine as it is.
Additionally, projectile should accelerate at longer distance, having 70% damage at short range and up to 120% at longer ranges, or 150% for extremely far shots.
Mercury should keep the 10 or even 15 more degrees turn angle, since it nerfed in other respect when close range.
What we get:
Snipers wars are funnier with screen shakes, gunners must time shots to win.
At long range, due to medium screen shake on ship movement, you can't really hit components unless you are really good or completely stationary. At shorter ranges, it is easier to do so.
If you CAN get close, you have a big advantage with gatlings. If you can't, you are in trouble, but one ship CANNOT keep firing indefinately at long distance without support, because the close range ship will eventually get close.
At short distance, mercuries are not completely useless. You get no screenshake if unzoomed, and the turn angle of the weapon allows for return fire.
Possibly not in this patch, but i think ammunition must change too.
I'd go for heavy (or something else) greatly decreasing jitter, decreasing rate of fire, slightly increasing damage.
One ammunition type should be for mercuries. I'm thinking penetration bullets
A new type of ammunition: it should create a small (harmless) white cloud where the projectile lands, impairing vision to other snipers if aimed correctly, but also leave a very visible smoke trails to bullets. Produce modifiers so that it mostly only feasible for mercuries.
I dont think it can be much more balanced than this.
