Aligning transfer ports of barrel and receiver

Any tips for reliably aligning a barrel so its transfer port lines up with the receiver's transfer port? How sensitive is it to small misalignments?

The breech end of my barrel is just a cylinder with no indexing marks or pins. There's a setscrew on the shroud that appears to be directly opposite the transfer port. I lined that up by eye with the screws on top of the receiver. It shoots consistently, but I don't know how to tell if it's shooting optimally.
 
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