Year ago and I do mean years ago when Pope was king of making barrels (Not THE Pope but Harry Pope). Gain twist was popular, even common. I think most of Colt's revolvers were all gain twist. Today, not so much but it may be coming back. The Smith & Wesson 460 XVR revolver has a crazy gain twist barrel, something like 1-200 down to 1-18...I think. I know that Bartlein offers gain twist, I believe Kreiger does now. Also, in the black powder world, Colerain offers a gain twist. There are probably many others but that's all that come to mind.
I went with a 5R gain twist 9 in 1 to 8 in 1 on the Bartlein I have on order. I Why? I've tried everything else under the sun and I'd like to try something new and Bartlein would never steer me wrong. It likely may not work any better than any other Bartlein or Kreiger barrel I have, which would mean they shoot fantastically, but it's something new to look at.