These are unique rifle and shotgun designs that are just as effective as any other rifle or shotgun design, the only difference is they have a slightly different appearance.
First, a shout out to @empty shadow for his idea to use #1271285696492994662 as a much more worthwhile unique weapon, when I was researching this idea I only picked a .410. While the .410 could use buckshot and slugs as alternative ammo and the pistol needs some love, a 20ga or 12ga would be way more effective.
Second in the line was the weapon that started this for me, the Rossi Circuit Judge. Originally a .45/.410 revolver it was converted into a rifle to become a more effective hunting weapon. It was offered in several different Calibers and even a 28ga shotgun. My suggestion would be a .357 since the .44 already got the lever action upgrade.
Last, and most unique, a Colt model 1855. This is a black powder revolver, it was offered in a lot of calibers that simply don't exist anymore. Despite that, I think a .45 caliber muzzleloader would be a great 3-7 caliber. As far as the reloading animation, I'd just suggest swapping the cylinder for a new one, it was common practice to carry multiple cylinders rather than trying to reload in a gunfight. If it was good enough for the James Gang it's good enough for us