Both my Turbo and my 40x have Broughton 5c's (one 17 twist and one 16). I got my Swindlehurst as a barreled action from Gene Davis and it has a 4 groove Broughton on it. All of them are in a Ross taper. Talk to Roger, I took his advice on the barrel for my Turbo (the 40x I bought from him already built) and have never regretted it.