I have a 300 Jarrett, built by Dave Tooley. I had another one that I sold to a buddy of mine last year. I have just started working on the load for the one built by Tooley. I' do not remember the twist, I told Tooley I was shooting 165 grain bullets, plan on using Nosler AccuBonds. The barrel is a Hart, the stock is a Lazzeroni sporter from McMillian, with a jewel trigger. I alos have a switch barrel in the Weatherby .257. Tooley talked me into it and I must say I have been very impressed. I'm going to go ahead and get Tooley to make me another .257 barrel for the gun. I hope to rat hole enough money to have him make a second gun latter this year.
The Jarrett I sold last year (was built by CPR) used 88 grains RL 25 pushing nosler 165 grain Ballisitic tips at 3500 FPS. It shot great off the bench under a half inch at 100 yards consitantly. I also use the 7 STW brass; had some issues with the Remington 8 mag brass.
Good Luck
SC