Right, firstly I'm not gonna call you a silly bunt for letting that happen 'cos you already know that.
Now you know why PB guns should be cleaned asap after shooting them, or at least pee down the barrel to loosen the fouling.
Remove the grips. Dump the gun in a bucket and cover with diesel and let soak for a few days. On removal, dry off as best you can then rinse in HOT water, now try dis-assembling and cleaning thoroughly. Hopefully the pitting won't be too bad?
Pistol & Rifle Shooting in the Highlands with Strathpeffer Rifle & Pistol Club. <StrathRPC at yahoo.com> or google it.
No longer Pumpin Oil but still Passin Gas!