Importing from Blender > Unity issue

Simply when I was importing my pistol model I had some weird issue with the Vertices, I’ve checked the bones used for rigging & animating by moving them away from the main model and with this No issues occur, though as soon as I import into unity this happens.
152854-capture.png

whilst in blender I have

I’ve discovered that the weights aren’t applied in unity, Though it is applied in blender,
So basically the bones have their “automatic weights” in unity but the custom weights in blender, Any idea how I fix this?

EDIT: This only happens with the FBX export, Which I use as I have animations that I want to take into unity.

Can’t see anything wrong at first glance either, but I’ve had plenty of issues importing FBXs! So I’ll try:

-I’m seeing in the Blender screenshot that the origin of the gun Object is not set at 0, are the Armature and gun Object on the same position?

-Have you checked in Blender if the Armature has its Scale applied so it’s set to 1?

-Do any of the bones are scaled or have scaled animation? Usually scaling stuff can lead to weird errors like this one.