Re: new 7mm sendero are the barrels unfired!
That chatter mark you said inside your barrel worries me, but if your rifle is still shooting MOA and under for 5 shots, I'd say you got a decent rifle.
I had a Winchester model 70 in a 7mm STW that had about the last 4-6" of barrel with chatter marks. Well mine didn't shoot for [censored], I was lucky to get 1.5" at 100 yards. Finally shot about 1" with 180g VLD's, but by the time that came around, I already had a buyer. The guy who bought it came with a borescope and we found the problem. I was upfront with him about it, saying it wouldn't shoot better then about 1.5" with hunting loads, but with the 180g Bergers, it would do about 1". He said it was good enough for him, so he took it.
On the other hand, my other winchester model 70 is a 25-06 and its one of my most accurate rifles. Go figure...