As stated above, the summer months are usually a dip in both volume and a slight retreat in prices. People are focused elsewhere. For non-collecting activities, I've observed spring as a bump and always felt it was for two reasons: 1) tax returns 2) hunting licenses; then a slow down mid-summer. I've watched prices for over 10 years running a site to track prices (example:
SKS prices, but will need to terminate the site this year once my hosting contract is over, just not enough revenue to justify it and kicked off of ad platforms due to the content being about guns. Not enough traffic to justify alternative ad platforms who require a minimum traffic level, and as stated kicked off of the 800 pound gorilla platform). Anyway, summer can be a dip and as with stocks, "buy the dip". General trend over the 10+ years I've run the site is up and if viewed as investments (I don't it's a collection for my enjoyment) every single purchase I have made is well over the dream 8% return (8% doubles every 10 years). Still buying when I spot something to fill a gap in the collection, but maybe not at the rate I was a few years ago. The items I'm buying now are higher priced, like a 1903 Springfield, so that helps temper the rate compared to buying interesting Mosin Nagants at Big 5 for $50 (actually picked up a hex receiver M44 for $50 at Big 5 years ago for $50!).
Another thing that will contribute to a slow down long term is a lack of youth getting into the hobby of collecting and shooting in general. So much easier to play a video game than all the work for hunting or even shooting for fun and cleaning firearms after the fun is over. Not my kids (to brag a little), who enjoy "hiking with guns" as my son calls hunting up until the point we find the animals and harvest to feed the freezer. Very few want to do all the work necessary to harvest their own food (and we smoked some excellent elk steaks last weekend and elk shisk-b-bob this weekend!). Collecting and learning the history is a hard thing to get some kids into and it is fun but hard work to learn. If I do ever let people see my collection, their first word (after wow...) is "arsenal" as that is how they have been conditioned to react through popular culture. It takes a while, but eventually everyone I trust to view the collection comes away with somethng like "it's a historical collection". Just recognize it's harder to collect and learn vs. pushing (monkey-click) a single button on an iPad until you get a dopamine rush. I feel it's better to work to know what you are looking at, and after maybe years of reading and learning find "the one" and bring it home, clean and shoot. Quite possibly, given the ammo situation, you'll have to buy dies and reload some new caliber, find a new powder, and a new diameter projectile to make the ammo to shoot a new find (maybe even fire-forming brass...)! That's a lot more work and time than downloading a new game.
I see the same with collector cars, kids just are not into it. Sure, there will be a demand for Mustangs and Corvettes for a while, but once the boomers die off I expect a slump. Who wants to hunt for, find and restore a 1967 AMC Marlin (one-off year for the body and parts are made of unobtanium!), or any other wonderful odd-ball? Car show attendance is down and the stuff that is coming is much more standard and has a narrow focus. I stopped attending mixed shows when people started sitting on the fender of one of my odd cars to take a picture of a 70s Mustang painted plum-crazy (a Mopar color) and telling me that Mustang was "restored".
Plus there are space concerns. To live like we do now, single-family, detached home, lawn to mow and maintain, with space to hold and display a collection, would require a huge investment. You'd be working for your house for years (maybe your entire career) to pay it off before you could play. We accepted that there would be some "wage-slave" years and that retirement would bring comfort, time to spend with kids, travel more and grandkids and enjoy hobbies. That deal is actively being destroyed. Look around in the cities and see all the apartments being built. The sprawl may have been unsustainable, but every day looks more and more like a dystopian movie (like Soylent Green, if not a more modern version).
Ugh, that's a downer. I'm going to go reload some odd caliber now and focus on some future fun shooting some old rifle soon.