Some of the .451 shooters I have dealt with found platinum liners. They will outlast any other metal by a wide margin.
The thing about how fast a vent liner erodes has to do with which brand/type of black powder you are shooting. What is the grain size and how big of a charge are you using. The gas temperature during the powder burn will determine how fast the liner vent erodes and grows larger. A rifle type black powder can produce a maximum of about 1800 degrees on the surfaces of the burning grains. A very fast and hot sporting type powder is able to produce a combustion temperature up around 2200 degrees. That will have a lot to do with how fast the vent liner hole is enlarged due to the heated gases and their scouring action. Why stainless steel vent liners generally outlast those made with softer steels. You see these platinum vents commonly used in good European flintlock guns. They used some very fast and very hot burning powders in those guns.
Bill K.
The ones I use are stainless, as I'm sure you know, just for clarity. They tend to enlarge in the slot first, so the hole is oblong, though I try to change them in my chunk guns long before it's visually obvious. I think the heavy charges and tight patching blows the hole out faster, but not like a bullet gun. Smaller calibers wear the hole faster as well, presumably due to higher pressure?
I know people using platinum nipples, also people who change stainless ones every match (it comes out cheaper sometimes). I would try a platinum liner or a beryllium copper liner if I could find a good source to know what I'm getting, but I'd he reluctant to give up the screw slot or some other convenient removal design
! I'd be embarrassing to state how often a new touch hole liner has been installed on my chunk guns. Cost is about the same as a flint (these days) and it has never hurt a string, at least.
