I'm looking seriously at a couple of Holland & Holland Royals as guns I can shoot as well as count as an investment
Speaking from a UK perspective and acknowledging that Toby and Dig know the market very much better than I do, this my take. You indicate that you want to shoot this gun, so go with the one that pleases you most. Your enjoyment will come from it's use, not it's resale value.
Having said that, should you decide to buy a best gun as an investment only, you surely must take into consideration your other investments, your portfolio in the round and your tax situation. In the UK guns are treated as a wasting asset, along with classic cars, fine time pieces and model railways (amongst others). Essentially the tax man recognizes that anything with a 'recognised lifespan of 50 years or less' is a wasting asset. Furthermore, when sold or inherited by one's heirs, they are free of our capital gains tax, usually paid on the sale of other asset classes, including stocks, bonds, property and so on.
I would therefore only consider buying best guns - Purdey (Woodward), H&H, Boss - as an investment if I was in the happy position of having to find a home for a great deal of money and where I needed to spread my risk into alternate asset classes. What a great situation to be in, I can dream now of my collection of wonderful shotguns, rifles, classic cars, boats and wine! Additionally, I think the key would be to invest in those guns that we know would
retain their value. If the value goes up during our ownership, so much the better.
By the way, I have nothing to do with the whole investment community, other than using it when I have to!
Tim