So I have my  8" titanium can with 304 stainless internals (formed cones from stainless plugs). The only two guns it is shot on are a .300 blk 10.5" with mostly subs and a .308 with a 20" barrel and a SDTA muzzle brake. If I keep shooting my .308 through it with supersonic loads am I going to wear out the can before 1k rounds or are the stainless cones combined with the muzzle brake acting as a sacrificial blast baffle going to keep the can near wear free? From reading and looking at pressures involved I think .300blk subs should not wear the can much if at all but does anybody have experience with 304 stainless baffles and full power rifle rounds?

Yes 304 will wear out faster then say 17-4, but no one can say exactly how long it will last. the life of a can really depends on how hard it's ran and what it's attached to (IE mag dumps on an SBR is going to wear it out faster then slow fire on a bolt gun). I wouldn't worry to much when you do wear it out, just send it to SDTA or Sirearms and get it re cored with their monocore, no new stamp necessary.

I would expect you would have noticeable wear before 1000rs of 308.

That's doubtful, I've got over 1k through my 12.5" AR15 and have minimal wear on my baffles. I'm also running standard, mild steel, freeze plugs with one SS blast baffle/cone.  20" 308, with SS baffles on a bolt gun. Thing will probably go several thousand before showing any serious wear and tear.

My blast baffle is .100" of inconel so it should last a while.

I have a 308 suppressor with maybe 200 rounds on all aluminum baffles I built cheap and shows no wear at all. I should add they are k baffles so might have different wear pattern than cones and they are pretty thick to help with compression of rifle k baffles.

I'm not sure if the plugs are true 304, the chinese producer may be using a pot metal mix that will stamp easier.  I formed the plugs in question and they were much, much easier to form than OEM Ford Stainless plugs (they were old stock, made in USA).  The current production SS ones in question lasted 700rds vs 400rds (standard plugs) for him.  I got similar life out of the regular plugs.  Others have had them last much longer, if your shooting slower, no sbr use, lighter loads, etc many variables can effect baffle life.  There have been bore pics of AAC Cyclones (308 with 304ss cones) that had significant wear at 1-1.2K mark posted here, and the AAC rep at the time called the wear normal.  I've drilled out 4140 Steel cones (along with many SS, Ti VSRS and cones) and the material seemed many times harder than the current market "stainless steel" plugs .

Where can you get stainless plugs? I've had no luck finding them in any size but 1.5"

You should not have an issue finding 1 3/8" also.

Adding some synthetic or regular 10W30 every now and then will make it a little quieter and slow down the harmful oxidation that occurs on carbon steel due to the heat and acidic gases.