hammerback, you are on the right track. The value of the gun comes from three basic factors; Brand Value level (BV) of the maker's/retailer's name, Original Quality grade (OQ) of the gun itself, and the Current Condition level (CC) of the gun today. "Best work" was not confined to some select few makers. It was a function of the price point of the gun. The local ironmonger (think hardware store) could order a "best work" gun with his name on it from a number of Birmingham firms. So, it is very important to keep the original quality grade of the gun separated from the brand value level of the name on the gun.
Looking at your photo, I see a Royal pattern action (based on pin placement), decent quality and good engraving coverage, good fitment, so I'd say it is a second or third grade SLE, lets say OQ2.5. Hands-on inspection might shift that some, but it should be a good start. The current conditiion looks to be around "significant use" level, so we can start with CC3. The Cahsmore name sells at brand value level 3, BV3. BV3-OQ2.5-CC3 = $6100; and a premium for 16 bore of, say, 1.5. Say around $9,000. If that price doesn't square with known reality, I may have had insufficient information from the single photo.
Does the wood quality suggest a higher or lower OQ grade? Are there other fit and finish clues as to OQ? Would the current condition fit better to a higher of lower level description? Is there a known selling price or asking price? Is 1.5X an up-to-date 16 bore premium?
