I was out in the desert firing my 6.5G build for the first time, last weekend. An upper with a 20" Ballistic Advantage "DMR" barrel. Nice weekend overall. I got to break it in, sight it in, and shoot it out to 1000 yds all in the same day! (Shot great, btw, but that's a story for a different thread.)
But I noticed that the brass is coming out with odd scratches on necks. They're all around the necks on all fired cases. It seems apparent that these scratches are occurring after firing because the scratches are superimposed on the black sooty stuff. I would guess that there are some slight burrs around that shoulder-neck transition, not pronounced enough to do anything when going into battery. But after firing when the neck gets expanded a bit, it's dragged across these burrs during ejection. Make sense to everyone else?
So, I am thinking I need to do a bit of polishing! What would be the best way to attack it? I have a Dremel. And I also have a drill with one section of cleaning rod that I can use to attach something like what's in the link below. Maybe A Swab-It, in .410 cal? Coated in some kind of polishing compound? It would be nice if I can do this job without having to remove the barrel from the receiver. But I am willing to do that and make it a more involved project if need be.
If you have adjustable gas on this rifle, turn it completely off and fire one round. Then slowly and carefully as can be extract it by hand and see if it still does it.
That will tell you for sure if it's happening when fired and the neck expands or if it is somehow happening during normal ejection cycle and that it maybe something different making the scratches.
That's a good idea, but I don't have an adjustable GB. Didn't need one. I suppose pulling the handguard and shifting GB fwd a little to block the hole would do the same. But i don't know when I'll be out in the desert again. I suppose I could pay to go to one of the indoor ranges in town.
But one thing you may not be able to see from those image is that these scratches have a very slight angle to them, a slight spiral. That's further evidence that they're occurring when the bolt is being pulled back and rotating. IMO.
My question is still focused on how to best to polish the chamber. I don't see how it can hurt. And I read in one of these threads in 65grendel forum, a post by one of the veterans here (can't recall who) said... "I would never install a Grendel barrel in an upper without first polishing the the chamber and feed ramps". I had already installed my barrel by the time I read it, so I decided i'd have to take my chances. Now it's looking like a little polishing is in order.
SDW Wrote:That's a good idea, but I don't have an adjustable GB. Didn't need one. I suppose pulling the handguard and shifting GB fwd a little to block the hole would do the same. But i don't know when I'll be out in the desert again. I suppose I could pay to go to one of the indoor ranges in town.
But one thing you may not be able to see from those image is that these scratches have a very slight angle to them, a slight spiral. That's further evidence that they're occurring when the bolt is being pulled back and rotating. IMO.
My question is still focused on how to best to polish the chamber. I don't see how it can hurt. And I read in one of these threads in 65grendel forum, a post by one of the veterans here (can't recall who) said... "I would never install a Grendel barrel in an upper without first polishing the the chamber and feed ramps". I had already installed my barrel by the time I read it, so I decided i'd have to take my chances. Now it's looking like a little polishing is in order.
You will probably have to remove the barrel to polish it, if so while it's out might as well polish the feed ramps as well.
Your right in the pic you can't tell they are spirled they look straight.
Technically I think I could do it using this method. In the picture is a section of old cleaning rod. If I use those bore sponges for the polishing then I would need to use this rod no matter what. And hitting the ramps with a Dremel with little polishing wheels would be super easy. But maybe it'd be easier to check my progress if the barrel wasn't in the receiver. Might be easier to clean up all the polishing gunk latter as well.
BTW, I did contact BA tech support about this situation. I admit that I do not understand this explanation they gave, but it doesn't seem to explain the how the scratches would get 360 degrees around the neck, and be scratched through the black coating:
"Marks like that happen when the round is feed into the chamber. This is due to the neck size of the brass and the way it interacts with the feed ramps. If you have a small Dremel, you can knock down the edge slightly to possibly keep this from happening again."
For as polishing feed ramps go it is much easyier to polish and then clean everything up with it removed from the upper.
Also plug the chamber with a earplug so nothing goes down chamber while polishing the ramps.
As far as the neck scratches and polishing that area. Me personally I wouldn't do it until I tryed firing a round with the gas off just to be perfectly clear that what you think is happening and causing it is what is happening.
I always like to eliminate everything I can before I go to tearing stuff back apart and doing any kind of work. Saves money and time.
Key posts in there are by kswhitetails and LRRP. Post #s 8 and 9 I think. good info. I couldn't do mine all pretty like LRRP's without pulling the barrel assy, that's for sure. I guess I should probably just bite the 'ol bullet. My resistance mainly comes from having a BCM KMR handguard. You ever install one of those? The fit on the barrel nut is ridiculously tight. I had to tap it with a plastic mallet to get the last half inch to go on. But maybe now that the inside finish has been burnished by the initial install, It won't be as hard to R&R the thing.
I see what you are saying about verifying this first. I will think about it.
BTW, I got my barrel out of the receiver. Took a bit of heating with my hot-air gun, but I could finally pull that handguard off the nut. LOL This will make the job so much easier.
