I would sell the Colt side-by-side on a specialty forum where participants know and appreciate what you've got. A SASS forum, perhaps. Otherwise, the more common stuff I'd probably list on gunbroker and just roll the dice.
FWIW, I have sold probably 80-100 guns over the past five years. I've tried various methods, including:
• Gunbroker -- hit and miss. Some stuff sold really well. Others attracted little interest. Auctions allow the market to set the price which can be a good thing or a bad thing depending on how the auction goes. FWIW, I usually set a reserve price, so that may affect how well my auctions do. Be aware, Gunbroker tracks sales tax and will hit your account for the tax owed on the guns you sell so make sure you collect that from the buyer. Also, fees are significant.This method requires some effort on your part in that you'll do better if you provide a bunch of good clear photos and write a good description. You also have to be ready to answer emails from potential bidders. One big downside to gunbroker is that you've got to ship the guns. Long guns are easy since they can go USPS but that won't work for handguns. Use the
shipmygun.com website to save a few bucks and avoid having to enlist an FFL to facilitate shipping handguns.
• Gun enthusiast forums (the EE on AR15.com, Shotgun World, the S&W forum, etc.) -- These generally work pretty well. I've had really good success with the S&W forum, but less with Shotgun World. A big advantage of these venues is that there's no sales tax or selling fees to worry about. Also, the participants often have a greater appreciation for what you're selling and often pay good money (this was especially true of the S&W forum). Again, you have to be willing to put forth the effort to shoot good photos and write a compelling description. You also have to be willing to set a price. The same issues with shipping guns apply with this method.
• Gun show -- I've set up a vendor table at a couple of gun shows. I actually did reasonably well with this approach. The first time I sold 11 guns in one weekend. The second time I think I sold six. I also moved some ammo, old scopes and accessories. The downside is that you've got to talk to yay-hoos, looky-loos and total dipshits for two days. Also, don't expect to sell anything too unique or sophisticated. Common stuff like Remingtons and Winchesters do pretty well. You've got to price to sell, though. Not the place to try to get top dollar. Advantages are no shipping, no paper-trail cash sales and you can "pass the trash" if you're an unscrupulous sort. There is some concern about the future of gun shows following the ATF's recent final rule on engaged in business. As it stands now, gun shows are still a go. Also, under any reading of the final rule, a guy selling "all or part" of his personal collection is absolutely allowed to set up at a gun show. Guys like you are not the target of this new rule.
• Consignment auctions -- Twice I've taken loads of guns to Bryant Auctions at the Lake of the Ozarks for their semi-regular consignment gun auctions. The first time, I sold 24 guns and came out about as well as I would have done listing them myself on gunbroker (factoring in fees for both). Some stuff didn't bring what I hoped, but others did much better. Bottom line, I was happy. Second time I brought about a dozen guns. There weren't many buyers and they didn't want to pay much. I felt like I gave some stuff away. This approach works best for common type guns. I had no luck with anything even slightly unusual. The auction house I used also sells ammo at their sales and I did really well moving a bunch of ammo. Like the gunshow sales, it's a once-done-it's-done kind of thing so there are no concerns about a buyer coming back to you after the sale. Also, the buyers have to do a 4473/NICS, if that matters to you. Auctions are another great way to pass the trash, again if you're inclined to do so. One downside is that it takes about a month to get paid.
• Direct to local dealer -- I've sold maybe a half dozen guns to a local dealer. This method is about tied with my second/bad auction experience for worst return on my guns. The advantage is that it's quick and easy and a done deal. Sometimes it makes sense, though.
BTW, none of the gun shops near me accept consignments. FWIW, when I was a pawnshop FFL, I didn't take consignments either. Be aware, if you consign your guns you've got to be OK with every half-wit stumpjumper and counter monkey finger fucking your gun. In the event that the gun doesn't sell and you want to try another approach, you'll have to do a 4473 and NICS check to get your own gun back. Most shops are going to want 20% or so to consign. Given that you get paid right away, it might make more sense to just sell it to them at a slightly larger discount.