MELEE:
In my own modding experience I found that the easiest way to make melee weapons work was to make them fast, powerful, and accurate. I let the soldier's attributes (like strength, melee accuracy, reactions) add most or all of its damage, meaning it scales in power with game progression or just with how often you use the weapons (especially if the weapon trains the same attributes it uses). My rule of thumb is that a given melee weapon should do more damage than a ranged weapon at the same tech level, even though it costs less TUs to use. Also consider how often it should actually hit, and adjust its accuracy accordingly. Vanilla melee accuracy is 20-40, so a melee weapon with a 100% internal hit chance will still miss most of the time.
Your Gauss Cannon:
Range: 25
Damage: 90
Accuracy: 35
Reload: 20/16/12
Effective DPM vs small: 62.4/78.0/104.0
Effective DPM vs medium: 70.9/88.6/118.1
Effective DPM vs large: 88.6/110.7/147.7
Your Sonic Oscillator:
Range: 50
Damage: 110
Accuracy: 40
Reload: 24
Effective DPM vs small: 72.6
Effective DPM vs medium: 82.5
Effective DPM vs large: 103.1
Your alien sub hit points:
Very Small: 50/60/150/260/350
Small: 300/500/650
Medium: 550/650/750
Large: 1400/2000/4200
My conclusion: the sonic oscillator has potential merit by having more range. Even if no USOs have a weapon range within the margin, it can still likely down small subs faster than the gauss cannon merely because it begins firing sooner. But even against the beefier smalls, the sonic oscillator is still about the same power as the gauss cannon. Mediums have roughly the same toughness as smalls, but against larges the sonic oscillator will be weaker unless you mount several of them. Short of mounting it on a Leviathan (or maybe a Manta with good torpedoes), the range advantage isn't going to make much difference against something that beefy.
There are four ships that can notably be out-ranged by the sonic oscillator (but not the gauss cannon) (and I have no idea how often they show up): Cruiser, Hunter, Envoy, Mothership.
The DPM values I put above are based on assuming no pilots, and running the full set of equations to determine average sustained applied damage. None of the craft have built-in hit bonuses that I can find, nor do any USOs appear to have dodge bonuses. Therefore, the addition of pilots to grant hit bonuses should increase all the DPM numbers somewhat evenly, with some advantage given to lower hit chance weapons (like the Gauss Cannon) and against smaller USOs. Based on this info, I conclude that you should probably make the following change:
Sonic Oscillator Reload Time:
24 => 22 (if it's supposed to be marginally better than Gauss Cannon)
24 => 20 (if it's supposed to be significantly better than Gauss Cannon)
24 => 18 (if it's supposed to be way better than Gauss Cannon)
24 => 16 (if it's supposed to be a supergun)
As for the ammo, you should just create a manufacturing recipe that turns Zrbite into Sonic Oscillator ammo. Maybe 1 piece for 5/10/20/25 shots.
