The formula is not all things to all people. Round Actions are outside the range of "usual." Note that I finished up saying that the Gavin Gardener estimate suggested a 94% premium on this pair; practically double the price of similar brand, quality, and condition SLE's. We shall see how these sell come mid-April.
Here is a pair of MacNaughton's (auction estimate of £12,000-16,000) that sold at Holt's for £13,000 (about $32,500 for the pair/$16,250 per gun) at the March sale. Formula: BV2-OQ1-CC4 = $11,938. Premium = 36% over formula. Are MacNaughton's priced less than Dickson's?
http://213.219.62.57/asp/fullCatalogue.asp?salelot=1016++++1317+&refno=+++15325&saletype=The formula can't give you exacting prices on everything. The market is way, way too complex for that. However, it does organize the market in a way that makes pricing much easier to understand (and remember) and it gives you a baseline for comparing guns outside the usual. Round actions are outside the usual.
Here is single Dickson from Holt's. Estimate £6,000-8000, hammer at £7,500 (retail USA = $18,750). BV2-OQ1-CC4 = $11,938. Premium = 57%
http://213.219.62.57/asp/fullCatalogue.asp?salelot=1016++++1418+&refno=+++15336&saletype=This MacNaughton failed to make reserve on an estimate of ,000-8,000. £6,000 reserve = $15,000. So, this gun failed to bring a 26% premium.
http://213.219.62.57/asp/fullCatalogue.asp?salelot=1016++++1418+&refno=+++15336&saletype=This Dickson hammered at £9,500 (estimate of £8,000-12,000) for a retail of $23,750. BV@-OQ1-CC3 = $15,686. Premium = 151%
http://213.219.62.57/asp/fullCatalogue.asp?salelot=1016++++1443+&refno=+++16040&saletype=Some people are willing to pay the premium and others are not. That is why we have a market. My point would be that you must be willing to pay a 25% premium above a best SLE for a MacNaughton Round Action and something over 50% if you want a Dickson.