AAA Quality Assault Rifle Asset Packs from Studios

Hey I have a question about this Weapon Mount bone you use for positioning the weapon mesh, First of all it shows on the skeleton that it’s zero’d out in same place as root bone aswell as the weapon socket, however the gun is seemingly magically set in the correct position on the arms mesh provided. However MY arms mesh doesn’t seem to have this magic, it uses the same skeleton as the arms provided but when I change the arms mesh from yours to mine in your character BP the weapon goes strait to 0,0,0 where the weapon mount says it is. It’s even correct in persona on your arms with the preview mesh and again not on mine. I guess my question is what is this voodoo your arms mesh has to make the weapon go to the correct position despite weapon mount being located at 0,0,0?