1878:
What are the stock dimensions? What does it weigh?
I have some experience with selling a custom single shot. In my case, it was a custom Ruger No. 1 in .270. It had a solid rib machined for the Warne QD sights, a 3 leaf rear sight, leather covered recoil pad, inletted safety button and a host of other features. I paid about $4300 for it; Hallowell took two plus years to get $2200 for the rifle 9 years later.
Based on my observations, unless the maker is a very famous name, you're looking at a about a 50% haircut coming out of the gate on resale.
By the way, I own a Greener small frame takedown in .22 Long Rifle on which the metal work was all done by Brian Burgin. It's a lovely rifle and I later traded a Martini Cadet in .218 Bee to Ken Hurst in return for his engraving the action.
Rem
