Eddie,
My Hart barrel is a 18.7" twist from late 1999. It is the first 18" twist made by Hart. After bugging them for a year, they finally made the button for me and sent me two barrels, saying the twist came out a tad slower than expected. The barrels were marked .3078" and 18.7 twist. I shot this barrel with 125 gr. Bergers (1" jacket) at New Braunfals. Most people would say that the .925" jacket would have been the better way to go, but it was this combination that shot so well back at the TX State match in 2000, with the first 3 groups of .150", .123", and a .190", that shook a lot of PPC shooters up so much.
I do have two 20" twist barrels that were made up by Douglas. I have never used either of these barrels in competition simply because they are not benchrest barrels. I bought them to test the idea of the 20" twist. I have shot .925" and 1" jackets out of them, and even though the stability factor for the 1" jacket is way lacking, the first group measured .170". I can say that the groove dimensions are the loosest of any 30-30 barrel I own, and I have some 7 ogive BIB's to try since they are the fattest bullet I have. You just never know, one day the Douglas barrel might make it to a real BR match. I do have plans to purchase a 20" barrel from either Krieger or Bartlein, or maybe even a 21" to 22" twist if I start playing with .850" to .875" jackets.
Michael