[ARC9 Weapon Base] gamemodes/terrortown/gamemode/player.lua:772: attempt to call method 'GetHeadshotMultiplier' (a nil value)
1. unknown - gamemodes/terrortown/gamemode/player.lua:772
2. FireBullets - [C]:-1
3. DoProjectileAttack - lua/weapons/arc9_base/sh_shoot.lua:684
4. DoPrimaryAttack - lua/weapons/arc9_base/sh_shoot.lua:509
5. unknown - lua/weapons/arc9_base/sh_shoot.lua:334

I've tried everything, removing penetration, etc and nothing works. The only thing that works is setting the headshot multiplier to a fixed value in the TTT files.