Basically use the same weapon in the forge to level it up. To get it to level 10 you would need 10 of the same gun ? Also maybe there could be a item you would need to forge it every level. Level 3 6 and 10 would give you perks the higher the level the greater the effect.
Medicallity : while holding this weapon you you get hp every 5 seconds. (Level 3: 1 hp,(level 6 2 hp), (level 10 3 hp).
Deadshot: increased accuracy after kill (Level 3: 3% accuracy, (level 6 5% accuracy), (level 10 10% increased accuracy)
Focused: reduced recoil while crouching (Level 3: 3% reduced recoil), (level 6 5% reduced recoil), (Level 10 10% reduced recoil)
Quickness: mobility increase (Level 3 3% increased mobility), (Level 6 5% increased mobility), (level 10 10% mobility)
vampyre: Every kill gives you health back (Level 3 5 health back) (Level 6 10 health back) (Level 10 15 health back)
Medicallity : while holding this weapon you you get hp every 5 seconds. (Level 3: 1 hp,(level 6 2 hp), (level 10 3 hp).
Deadshot: increased accuracy after kill (Level 3: 3% accuracy, (level 6 5% accuracy), (level 10 10% increased accuracy)
Focused: reduced recoil while crouching (Level 3: 3% reduced recoil), (level 6 5% reduced recoil), (Level 10 10% reduced recoil)
Quickness: mobility increase (Level 3 3% increased mobility), (Level 6 5% increased mobility), (level 10 10% mobility)
vampyre: Every kill gives you health back (Level 3 5 health back) (Level 6 10 health back) (Level 10 15 health back)
x2
x1