Gunsmithing DPMS 6.5 creedmoor Barrel with off center chamber?

[InkedIan]

I received this barrel today and during inspection I noticed something that's bugging me. It appears that the chamber maybe cut slightly off center.... I'm seeing an edge at the beginning of the throat/lands and it's on one side but not the other. Here are some pictures of the throat at different angles. Opinions please? (gunsmiths preferably)

 

[stockdoc]

A bore scope would give you a better view. Do you have access to one?

 

[InkedIan]

No, the problem I'm speaking of is visible in the pictures though. The first 2 pictures show the side without the edge/lip and the next 3 show the edge/lip. Any gunsmiths out there seen this and is it a problem?

 

[InkedIan]

Has anyone seen this before?

 

[300sniper]

That is about the best picture I have seen demonstrating what I've tried to describe about concentricity when looking into a chamber. On a precision rifle, the transition between the fb/lead and the groves in the barrel should be uniform all the way around. Even with the naked eye, rotating the barrel against a light, you should see just a RCH transition all the way around. If you see none on one side an a heavy transition on the other side, obviously it is not concentric.

Truthfully, I don't follow the AR world so I don't know what you are paying for and what to expect out of a DPMS.

 

[Killswitch Engage]

How does it shoot? Not saying it's right or perfect but I would lay
money that you can't see or tell the difference shooting it. It's a mass produced rifle. It's gonna happen

 

[InkedIan]

I haven't installed it yet. Deciding on whether to send it back or not. I think I will since DPMS said they would look at it. I would just hate to waste the shipping money only to get the same barrel back or one just like it...

 

[InkedIan]

Well, sent it to DPMS.... We'll see what they say...

 

[hdbiker1]

Don't be surprised if they say it falls within their specs. But then again they might not.

 

[GH41]

Did you expect more from DPMS?

 

[InkedIan]

Did you expect more from DPMS?

Yes, as i've had a hand full of dpms' that were very accurate and didn't have this problem. We'll see what they say.... Wouldn't think they would tell me to send it back if they didn't see a problem. (I sent them the same pictures)

 

[jonaddis84]

While I agree that there is concentricity issues here, I can't figure out how this could happen. If a piloted reamer, there should be no way this can happen since that fb to leade transition is cut by one tool, even if the barrel was .2" off from concentric in the lathe. You would instead just end up with a way oversize chamber.

The only way I can see this in my head happening is if the reamer pilots center was not ground concentric, and the pilot stayed fixed without rotating in the bore. This would cause the reamer to rotate off center cutting deeper into one side and shallower the other.

Thoughts on that hypothesis? This has been bugging me since it was posted...

Sent from my GS5 on Tapatalk

 

[hdbiker1]

How about a bad button?

 

[DAVETOOLEY]

That is about the best picture I have seen demonstrating what I've tried to describe about concentricity when looking into a chamber. On a precision rifle, the transition between the fb/lead and the groves in the barrel should be uniform all the way around. Even with the naked eye, rotating the barrel against a light, you should see just a RCH transition all the way around. If you see none on one side an a heavy transition on the other side, obviously it is not concentric.

Truthfully, I don't follow the AR world so I don't know what you are paying for and what to expect out of a DPMS.

+1 on the pics. That's what I preach when I tell people all you need to check chambers is a $20 watch makers loupe. It is off center enough to have at least on land come all the way back to the neck. Not good at all. There are many contributing factors to a chamber like this. Barrel setup, it is an AR barrel and they don't cost much compared to a match bolt gun barrel so sometimes you get what you pay for but it should be better than that. Reamer or reamers used to cut the chamber. Piloted or non piloted. Barrel straightness. Rigid or floating reamer holder. Take your pick. It's not hard to do but at the same time it's not hard to do correctly. I've seen some odd shaped grooves from lapping but buttons are round and the groove is uniform because the land is what's formed in the rifling process.

 

[Gene Poole]

A non-piloted reamer? No reamer at all (CNC)?