Having been responsible for producing high-dollar auctions for several years (not gun related, but just about everything else), I am here to tell you there is no way to reliably predict auction prices. Most items I sold, by policy, had to be appraised before the auction sale and seldom were the appraisals anywhere close (in either direction) to the final hammer down price. I remember one auction selling six Rolls Royce cars where the appraiser hit within several thousand dollars of the winning bids, but that appraiser was probably the foremost expert in Rolls Royce prices in the USA. And he operated from a small town in Ohio.