Weapon models by BIS. They have 5 different LODs, View-pilot and memory, nothing else. 0 LOD has less details as View-Pilot.
In muzzle flash selection “zasleh”, there the shadow should be off and User: 0 to prevent the muzzle flash to be in the shadow. Selection zbran is where the weapon is.
All SEB weapon models had User: 0.
You need a Res LOD in your P3D with ~300 faces. You may set a named property for all higher LODs with more faces to: LodNoShadow=1.
I have a system for making weapon LODs:
View Pilot: max 800 poly (lodnoshadow - 1) LOD 0.1000: max 500 poly (lodnoshadow - 1) LOD 0.5000: max 300 poly LOD 0.7500: max 200 poly LOD 1.0000: max 100 poly LOD 1.2500: max 70 poly LOD 1.5000: as few polygons’ as possible
This way the weapon should work fine and cause no lag.