Jake - I have a market model for Brit-Continental, SXS, 12 gauge, typical models (there are some that fall outside of it), 1890ish to 1960ish, and USA retail. The model works of three parameters - brand value (BV) based on the maker's name, original quality grade (OQ), and current condition (CC). The model can be used to predict price based on the three parameters or to help estimate the parameters if the price is known (unreasonable price will produce unreasonable parameters). The model was developed to jump-start understanding of the market. It is an Excel file if you run Excel (PM me an email address) of hardcopy (PM me a land address).
BV has five levels from Brit top makers to Continental "guild gun" no-namers with a range in price of eight fold and is covered in a chart. OQ ranges from "best quality SLE" to colonial/farmer grade BLNE with a 20 fold price influence over nine steps. CC ranges from pristine to wall hanger over nine steps and has a twenty fold price influence.
Drop a note if you are interested.
