First off you need a gun model, I tried downloading a few free ones but as always you end up spending more time trying to crowbar whatever you find into shape, than you may have done modelling from scratch.
I created a very rudimentary shotgun shape in 3dsMax from a cylinder. Once you have this you need to add a Skin modifier to the mesh then add to this two bones. The bones will be identified in UnrealScript so if you are going to write your own then they can be whatever you want but if you're reading this then I guess we follow Epics lead.
The first bone wants to be the root bone and will ideally be inside the handle of the weapon (think of it as where the players right hand will be) the second will be along the barrel (players left hand)
These will need to be named 'b_gun_root' and 'b_gun_lefthand' Rig the bones so that all vertices are weighted completely to the 'b_gun_root' bone and none weighted to the 'b_gun_lefthand'
Following this add an Unwrap UVW and export the whole thing out as a .fbx file then go into UDK and import the fbx file into your package.
- Create / download 3d model
- Add Skin modifier
- Add 'b_gun_root' bone weighted to 1
- Add 'b_gun_lefthand' bone weighted to 0
- Add Unwrap UVW
- Export as fbx
- Import into custom package in UDK