A very inexpensive way to get in to the single shot set-ups is the CVA Scout Pistols:
357 Magnum and 44 Magnum. They also have some with bottleneck cartridges. They typically shoot great for the money.
CVA Scout V2 44 Remington Mag Pistol - 1 Round, 14" Barrel, Polymer Grips, Stainless/Silver
The FA single-shot pistol can be purchased with a 357 Maximum barrel...(y)
I would go with the 15" barrel, since you are wanting to stretch things out.
https://www.freedomarms.com/product/model-2008-single-shot-handgun/
The 357 Max will work with a Contender frame or G-2 frame.
You could also do it with a Encore frame...It will be heavier which could be a good thing or a negative things, depending on what you want to do with it.
If you get a barrel from Bullberry, MGM or SSK you can choose your barrel length...
15" 223 Remington with the 77 Grain TMK in my rig runs 2675 fps.
Customized center-grip HSP. At my elevation it stays above a 1800 fps impact velocity just barely beyond 500 yards
It shoots Great!
It is easier with a single shot.
You only have one chamber versus 5 or 6 with a single shot.
It is easier to get a field rest with a single shot.
There is no cylinder gap performance loss with a single shot.
Shooting steel from the bench at distance (500 yards) with a revolver is one thing...I had sighter shots to get on steel. Shooting from field positions with a revolver is a lot harder
Do you want a single shot or a revolver?
A single shot in a 357 Maximum (14-15") barrel will probably be flatter than about anything.
You can run Cutting Edge hunting bullets at ridiculous speeds since they are lighter and have less bearing surface.
For high Speed with a lower weight bullet...