Mutable skeletal mesh merge ignores attachment bone offsets unless reference poses match

Development Character & Animation
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1

I am building a modular weapon system using Mutable and the Customizable Object Plugin.

The Issue

My Receiver (Base) skeleton defines a barrel bone at (0, 5, 5),

Root

├─ barrel (0,5,5)

├─ scope

└─ other attachment bones

but my Barrel Attachment is authored at (0, 0, 0) for reusability.

Root (0,0,0)

└─ barrel (0,0,0) ← mesh weighted 100%

  ├─ muzzle

  ├─ side

  └─ under

When merged via Mutable, the Barrel mesh appears at (0, 0, 0), ignoring the Receiver’s bone offset. It only aligns correctly if I manually match the attachment’s FBX bind pose to the Receiver’s specific coordinates.

Goal

Ideally, the pipeline would support:

Reusable attachments (barrel, muzzle, scope)

Attachments authored at (0,0,0)

Receiver defining the attachment offsets

…without duplicating offsets in every attachment FBX.

Any clarification on how Mutable handles reference poses and skeletal merges would be greatly appreciated.

Thanks