Lewis, I am test shooting some Lehigh 17-4 Vent Liners in two different Knights. These Vent Liners are not even heat treated... I begged my way into testing them just see how long a 17-4 liner would last. One of them being a 1/20 Knight Super DISC. I have 104 shots with 120 gr, BH by volume and the 260 grain sabotless bullet. I am sure I am getting close to max pressure and yet the liner sill measure 0.031. I am sure a 17-4 Heat Treated will last much longer than the one that I am using. But, right now I guess I can not even guess how many shots that liner is going to go. 17-4 is more expensive than 416 - but it last much longer. - I like it!