I can't speak for the 17 Mach IV, but I have a 17 AH Stainless Bullberry 14" that is a great barrel. Bullberry cuts tight 17 AH chambers because Fred Smith, the owner, has a lot of experience in shooting (in the 10's of thousands of rounds) the 17 AH and that's what works best in his opinion, I certainly agree with him from my own experience with his barrel. The cases will last a long time and my Bullberry barrel is extremely accurate, generally in the range of .5-.75" at 100 yards. At 17 AH velocities, a barrel should last about 10 lifetimes. If you decide on the 17 AH from Bullberry, let me know and I can steer you toward some loads.
Don't let those who really don't have any experience loading the 17 AH give you any BS about how hard it is to form the cases. You don't need anybody's special tool for $25-50 extra dollars, you don't need to do special annealing processes, you don't need to put X grains of fast-burning powder in the case and top it off with a wadded up paper towel - that's all a bunch of crap. All I do is use Imperial Sizing Wax and run the .22 Hornet cases through my Redding full-length sizing die, throw in my fireforming load with a 25 grain Hornady hollow-point bullet and go hunting, the fireform loads should give no greater than about 1.5" groups at 100 yards. Don't trim for length if you don't have to until after fireforming. The best accuracy advice I can give you is to use small pistol primers rather than small rifle primers in the 17 AH - try it, you'll see what I mean.
Good luck with your choice.
Javelina
