If you want to skip the prelim info please skip down to the spent brass in question.

This is a 5.56 parent case wildcat trimmed a bit and necked up for 6.5.  Member Dr69er has been working on it.  Barrel is an 18" mid gas from BHW that I had converted for my MRP upper by DBMG.  Also had DBMG put on the Noveske switchblock.  I got my dies and a selection of 20 test rounds from Dr69er on Friday and shot the first 10 on Saturday.  I sighted in at 25 and Chronoed the 120 grain HotCors.  Was running an FA carrier and H2 at first shot but did not cycle so put in a standard carbine buffer.  Ejected but still did not strip a round.  

First 5 rounds w/ 120grain HotCor (these were over H335).  Was anticipating 2400s given results another member with an 18".

2283
2271
2248
2275
2279

Check out the trimmed but not yet sized brass on the left.  

Trimmed 5.56 (to 41.65mm vs 45mm), 85 grain Sierra Varminter, 95 grain VMAX, 120 grain Speer Hot-Cor





I'm concerned about these consistent raised welts on the brass.  Does it suggest a rough chamber?  Does the barrel need to go back to BHW?

Have you tried to shine a really bright light up into the chamber of the barrel? It is a strange welt on those cases. And I am seeing what looks like a ribbon that drops down and crosses over it's self.
And the cross over point is at the same place as the ejection scratch on the case's mouth. I am leaning in the same direction as you, a rough cut in the chamber. Weather or not you see any thing looking into the chamber. I would consider sending back the barrel along with 2 or 3 cases.

Get a fine piece of wire or a dental hook type tool and see if you can feel any ridges (assuming you can't see anything with the light).

There's got to be a problem with the chamber given the consistency of the brass markings.    

You could even mark the end of the brass when chambered as a reference (ie a mark at 3 O'clock pointing at the ejection port), fire two or three rounds this way and I'd bet a dollar the cross-type markings line up exactly case to case.

Thanks all... will yank the barrel and try to get a picture of the chamber.

Attempt to retain capacity.  

Was not able to get a picture but was able to clearly see the rough ribbon looking cross cut in the chamber at about 5:30 though the band appears to go all the way around.

Would a polish likely be sufficient?  The welt is meaningful enough that I'm thinking it might require a new chamber (though my experience with these issues is limited).

Even if you could polish the chamber enough for the marks to be removed you are going to have other issues. The chamber is going to be much larger than spec and you are going to work your brass  really hard. That is if they don't fail immediately from the excessive space. There is no way I would try to polish a galling that deep out.

I suspect they are going to have to set the barrel back and rechamber it. That is a lot to take off because it is on the side wall of the chamber. Once they are done they are probably going to have to redrill the gas port in another location after they get the extension in place and the headspace set. And they may have to drill and tap the old port for a setscrew to block it off depending on how much they wind up taking off the chamber end. It also might take some maching on the barrel shoulder for the extension to get to the proper headspace.

Definitely a lot of fixing that will need to be done.

Dolomite

Looks like the reamer caught a chip and gouged the chamber. I would have trashed that barrel.

I'm going to ask for a replacement.  Sucks because I had them send it directly to DBMG for MRP conversion and switchblock install.  That process will have to be repeated.

Not out of your pocket, I hope. That's some shoddy work.

That's my guess, as well.
Whomever chambered that barrel is responsible for a new one, and all related costs, including shipping both ways, etc.
I wouldn't settle for anything less.

Will get a custom Lee FCD to alleviate potential issues.

Spoke with BHW and they say they will take care of everything (will see).  Will ship the barrel back tomorrow.  Thanks to all for the input.

Good for them for standing behind the product.
Stuff happens; it's how well they deal with it that separates the wheat from the chaff...