I got approx 2600 rounds thru one of my Coopers (204). My standard load was Sierra 39 gr, with Benchmark, at a LOT less fps than you're shooting. Barrel was a real tack-driver, but when accuracy quit, it quit. I couldn't hit a 8x10 piece of paper at 200! I sent it back to Cooper for a re-barrel. This bbl is accurate, but as much as the other.
My other Cooper 204 got 3300 rounds thru it before a re-barrel. I shot 32 gr Sierra Blitzkings with Benchmark thru it too. I had it bore scoped before re-barrel and throat looked like "rough pavement". However, it would still shoot 1/2" at 200 yds, and lasted two more prairie dog trips. I seated the bullets out a little longer, and it helped (this gun, not the other).
I would seat the bullets out longer, do a REALLY good cleaning, and if that doesn't work....time to look for a new barrel.