I just talked to Bobby today about sending him a 15/16" barrel to rebore for me. FWIW, he told me the largest he could take it is .54. I'll have to pack it up when I get back from a trip next week.
Here's a couple of pics with the buttplate off. I think you can see the gap better. If it's not apparent, it seems that the low spot is more prominent in the right picture, the lock side.