I had a 24ga very briefly. picked it up at a Cabela's Gun Library. It was a Beretta. But being a fan of one much more common ( but still oddball) gauge-- the 16-- I decided that one was enough.

The 24 looks to me like one of those answers to questions no one is asking. For those more in the know than I am, please chime in:

The 24ga is strictly a 2 1/2" deal. So you have a shell that won't hold as much shot as a 28ga (and that's without counting the newer, "magnum" loads.) So if you are already a member of the 28ga club, you have a gun that is far more versatile and practical than a 24.
Other than owning a gun that hardly anyone else has, the 24ga simply doesn't make sense other than as something quaint and quirky.

If you already are a 28ga owner, there is the definite possibility of mixing ammo if you're not careful. My gun came with 2 boxes of shells. I figured I'd shoot a round of skeet with one box and then share the experience with guys who wanted to take a shot. I got down to my last round. It seemed to stick a bit in the chamber. But luckily for me, it fired OK. But I then discovered that it was a 28ga. I must have had one or more of those in my "spares" pouch on my shooting bag and grabbed it by accident. Too close for comfort.

If you want something with a bit more punch than a 28ga, you can always look for a vintage, American 2 1/2" chambered 20 ga. RST offers a wide variety of shells. Even including quirky stuff, like spreader loads. Or an older, short- chambered European 20ga. I own a neat little Ithaca 4E 20ga. It has 2 3/4" chambers. As a 1920 vintage gun, it would have left the factory with 2 1/2" chambers unless it had been ordered with longer chambers which didn't become standard until several years later on Ithaca 20s. It's going to be strictly a grouse and woodcock gun for me other than maybe a round or 2 of skeet before the season, so I'll get by with RST's. And still have something that very few other kids on the block have.