I've done a comparison video showing your plasma weapons performance against vanilla gatling guns, and well, it's abysmal. The slow projectile speed and rate of fire indicate a high damage per shot weapon, so I multiplied the damage a factor of 8 to give them more or less the same performance (in terms of penetrating the armor wall in a certain amount of time) as the vanilla gatling guns while leaving RoF and projectile velocity untouched.

Video test footage: https://www.youtube.com/watch?v=0zpZwHUDynI

Dual25mm plasma cannon:
<ProjectileMassDamage>30 --> 240
<ProjectileHealthDamage>55 --> 440

40mm plasma cannon -
<ProjectileMassDamage>60 --> 480
<ProjectileHealthDamage>105 --> 840

60mm plasma cannon -
<ProjectileMassDamage>150 --> 1200
<ProjectileHealthDamage>200 --> 1600

Keep in mind while their on paper DPS is on par (well actually slightly worse) with the vanilla gatling guns against a static target, because of the low rate of fire and projectile speed, it is going to be a lot harder for you to land projectiles with these weapons on moving target in a dog fight, so their realistic DPS is going to be worse. You might even want to raise the damage beyond 8x base (maybe x10 or 12) to make them trade off vs vanilla gatling guns. But if you are not sure about that yet, 8x base damage is at least usable unlike what it is now.