How to Combine Armatures (Gun Armature and Arm Armature)

Question

I have 2 Armatures from separate blend files:

File 1 - Armature with a gun mesh that is rigged but no animations;

File 2 - Armature of an Arm mesh that is rigged with a reload animation.

The idea was to:

1. Prepare weapons individually.
2. Open the reload animation file.
3. Append the gun file to the animation file.
4. Customize the reload animation file for that specific gun.

This allows me to use the reload animation as a starting base that I would begin animating from.

How can I achieve this?

The 2 armatures after appending:

Another view of the Gun Armature mesh with vertex groups and bones. Arm Armature selected to show I've prepped a base reload animation that I intended to modify from.

Edit: I saw this post which describes selecting 2 armatures and joins with Ctrl+J but it will unfortunately break my animation. I want to add the Guns bones to the Arm mesh to preserve the current animation of the arms and then add the gun animation afterwards.

Edit2: I saw this post which suggest you first select 2 armatures -> join with Ctrl +J -> select the mesh and Armature -> Parent to Armature -> No Deform. It works okay, but for some reason the gun's Mesh and Bones are misalign/ exploded in Object Mode (Circled in Red). Im unsure why this is. Is there a way to preserve the gun's mesh and bones so that it looks like the first picture prior to joining and parenting the gun?

Answer 1

After some time I found out a method to do this while preserving the original reload animation of the hand and arms. If anyone has a better approach I'm open to suggestions.

1. Import Main Arm Armature: *File>*Open Blend File (the armature rig with hand and rams which the gun will be added)
2. Import Gun Armature: File > Append In File Browser Select the Second 3. Separate Mesh From Armatures: Select All Meshes (⇧ Shift + Left Click In Heiarchy), then in View Port Right Click > Parent>Clear and Keep Transforms
3. Join Armatures: Select Both Armatures, Right Click and select Join (Ctrl + J). Ensure you select the Gun first followed by the Arms. This is important as our Arm Armature contains animations while our gun does not.
4. Fix Gun Armature Bones: Select Each Gun Mesh(s), go to Modifier Properties> Armature > Set Object as Armature (the join previously cleared out the old armature entry).

After joining you may notice the gun may be oddly positioned. To fix:

1. Select Armature>Select Bone> Go To Pose Mode
2. For Each Gun Bone do the following:
   1. Go to Bone Constraints Properties
   2. If "Child Of" constraint then: Clear Inverse > then Set Inverse
   3. If no Child of > Add Child Of Bone Constraint > Click Set Inverse Begin Posing: Select Armature>Pose Mode> and position Gun to hand and begin animation