First it's hard to say, without knowing what the other guy realy did to it. That much fouling sounds like more than 20rds went through it but it's hard to tell. I never had that happen but I suppose it could with a softer copper jacket and a real high velocity. The most I've fired through my 300WMag at one time has been 40rds. What worries me is the groups opening up that much at 200yds, I would expect them to be 1-1/2" or a hair bigger. Is the ammo your shooting factory or handloads? If it is factory I can understand that performance. I've never been a fan of factory ammo for accuracy even the "premium" loads. Your weight of barrel should allow for enough cooling not to affect those groups. I'm thinking the bore may be a little bit rougher than most Rem.s. I'd try another break in session of at least 20rds. If he didn't break it in right it ain't ruined; probably just needs to be cleaned out completly and "re-broke in".