What is the difference between these two cartridges? Is one harder on the barrel than the other or foul more? From what I have read there is no brass readily available for the FB (Mach IV) but that should change in a year or so if this cartridge becomes popular. I kind of like the idea of a 17 cal center fire for the varmints out to 300 yards (proper conditions), watching the hit in the scope and low reloading cost.