I know of no gain twist barrels being used by any of the top shooters in 22 rimfire benchrest. The fad barrel now in that game are MI or minimally invasive rifling. Just a fancy way of saying shallow grooved. A few years back folks experimented with slow twist barrels on the very edge of stability from 1/17.5" to 1/19". Some worked well in warm weather but when it got cold they would keyhole. I in 16 or 1 in 16.5 twists are pretty much the std.. Folks in that game will use everything from 2 to 8 groove barrels. My best barrels were a Broughton 5R 1/16" sporter barrel and a Rock Creek 5 groove 1/16" both hand taper-lapped. I did have a Shilen Ratchet barrel in 1/16" that was almost as good as the Rock Creek..
