The shop responded over the weekend and I was impressed with the owner's consideration and his in-depth explanation. Good customer service, in my opinion. Here's his response to my query, in which I did indicate that I didn't know exactly what I was looking at and would appreciate some insight.
I would be really impressed if we were "good" enough to put that even a coat of cerakote down a bore without it building up excessively on the face of the crown. I bought Sata detail guns for our C/K work. They'll adjust down to a fairly narrow spray pattern, but not that small. This would take an airbrush and although we have one, there would be no reason to use it on a barreled action of a single color.
In the photo you sent us showing the discoloration you can see a very faint edge break right at the intersection of the crown and the bore. That edge break is the result of the silicone plugs we put in the muzzle end of the barrel when we blast/degrease/spray. The plugs are tapered slightly and when compressed in the hole the immediate exposed portion bulges slightly, creating the faint edge of uncoated steel.
I imagine there are folks out there who have goofed with C/K and accidently applied material up in the chamber/bore area. To date, we've never had this happen.
You also mentioned that the chamber is shiny while the muzzle is not. Consider that we conduct 90% of the machine work when fitting the barrel on the chamber side. One would expect to see a bright surface finish on any of the features we machined. The muzzle however is very innocuous by comparison. All we do is indicate the bore and cut an 11* crown. Had we not cerakoted the face of the crown, you would see a bright finish there as well.
I'm sorry but I don't have an explanation as to why your barrel is fouling or where the discoloration is coming from. Rock Creek's stress relieving process may have something to do with it. If the barrel is "cooked" after final lapping it would be expected to see a change in surface color. -The fact that the breech end is bright/shiny is clear evidence of this as we would have been removing the "stained" portions during fitment to your receiver.
As for the copper fouling I look at it like this.
1. Is the fouled bore creating any sort of issue with the overall functionality of the rifle?
1a. -Accuracy problems
2a. -Pressure indicators on brass, specifically primers going flat/cratered or ejector marks
3a. -Is there any sort of functionality problem such as hard extraction, sticky bolt, difficulty chambering?
If the answer to any of these questions is no, then I don't see the problem and I continue to shoot the rifle. I personally don't subscribe to this notion that guns have to be cleaned with the obsessive/compulsive behavior so common to the firearms community. My PRS rifle goes between 600-800 rounds before I ever put a patch down the bore. -And even with that I only do it because I start to feel guilty for "neglecting" it. The rifle shoots very well and has done so since it was first built early this past spring.
My gut says that you don't have a problem. Go shoot the piss out of it. If it runs the numbers then its not broke.
So, I'm going to go shoot it this week and see what's happening. The black bore thing really threw me, but maybe it does have something to do with a process used by the barrel maker. I'll report back with how things go.
