Bart, I had some very exceptional results with a RAS Tuner brake on a 6 XC, which to date is the most consistently accurate rifle I have ever fired, including dozens of 6 ppc barrels.
My first tuner was not intended to be a tuner, late 80's. I wanted to reduce muzzle flip on my unturned blank, 243 AI shooting 70's at 3850. The barrel was threaded 32TPI, and I made a huge collar with a single set screw in the collar, collar was made out of Brass. I threaded about 8" of the barrel, plus a long heavy Muzzle break. I wanted to see if the position of the collar on the barrel would change muzzle climb so we could detect hits better, which it did.
I had no idea or concept of a tuner at that time, never heard of one. I noticed the groups change in relation to the position of the 2" piece of brass that was 4" long on my barrel. Then the groups got down to a single bullet hole. We did get a lot of reactions about the brass collar from the Ranchers as they came out to socialize with us on the dog town.
Later on, I bought a New Savage Pump in 30/30 in an auction for dirt cheap money. It took lots of effort to get 2.5" groups out of the Savage, then I put a Limbsaver Doughnut on the barrel, made a few adjustments in 1/2" increments, groups got down to 3/4". It was then that I thought that there maybe more to this Tunner thing.