Firearms are balanced very carefully due to the heavy increases in their power.
Guns made from superior materials get a few bonus points in damage but not a ton. Imperial steel guns use 21st century but get a few extra damage points.
Dispersion is always better on any essence-based weapon just due to materials used. MAG and recoil dampeners will also affect this.
Essence-based ammunition can only be fired from guns made from Adamantine/Shadowsteel, these bullets are so powerful it would absolutely destroy the gun in one round if it was made from steel. This goes from irreversibly damaging the rifling thus rendering it mostly useless to a player, which I can't model, up to and including destroying the barrel or cracking the bolt in half. Since I can't and won't model any of that, you're just forbidden. Feel free to Pull Request to model these failures in the main game and patch it into the mod, it would be a lot of work for you to fire a bullet out of a gun once.
Both MAG components and recoil dampeners are hard to make
Knight Killers are due for balancing, currently uncraftable they will one day take extremely specialized esstech components.
Recoil is to be determined.
Enchantments shouldn't increase bullet damage on SGA weapons. Recoil, dispersion, or accuracy should be changed carefully. You don't use a telekinetic spell when a MAG component is used. Enchantments overall should be EXTREMELY CAREFULLY BALANCED. Adding insane power to already insane weapons would cause massive balance concerns, so I would focus on changing properties that don't affect combat performance, or that add new features and new attacks. An underbarrel mod that shoots fireballs can be called a "Firearm fireball enchant" and is a good way of adding combat effectiveness that doesn't change final weapon DPS.
MAG bonuses:
20% more damage added to the weapon approximately, based on the better between JHP and FMJ 25% more range added to the weapon
Essence Ammo bonuses:
25% more damage generally rounded up 20% more Armor penetration generally rounded up
5mm: 9x19mm 8mm: 5.56mm 12mm: 12.7mm 18mm: 12 gauge 20mm: 10 gauge