I would rather have $600 invested in the stock market for that time frame. Gun "investments" are all about quality, desirability, scarcity, and don't forget... the right buyer who sees the value of what you have. The 586 is quality; and probably has some scarcity in the excellent condition; but I'm not sure how many people will desire one in 8 years (at least for a premium price).
I knew a guy who had an investment piece in a LNIB Wildey handgun. Even though it was something that a lot of people desire and is of good quality, it was in 45 Win Mag, not 475 Wildey. For buyers, it's one of those things where if you're going to drop that kind of money on a Wildey, most people want the "Bronson gun" in 475 Wildey. Gun investments depend on people's tastes, which are very fickle.