AR15 Barrel cant?

[wintersborn]

I believe my new guns barrel is canted or will not seat in proper alignment.

The gun is new and was built by SBR from a complete CMMG bull barrel upper. I purchased and installed a Troy 13" extreme rail that is free floating with a Troy barrel nut. The install was done properly and seemed to fit just fine and the rail lined up flat with the upper etc.

I took it out to sight it in with irons (Troy) and a scope (konus M30) as well as broke in the barrel. I found that at about 25-30 yards it would shoot so far to the right that I almost ran out of adjustment on the rear iron sight to compensate. The groups were tight with no flyers just off to the right. I then installed the scope and ran out of adjustment and had to hold over 4 dots (mil) to compensate for it again shooting to the right.

It must be this no name scope mount I thought so I stole my buddy's Weaver tactical rings and it again shot so far to the right that I was almost out of adjustment but this time with no hold over. So partial POS mount issue but the fact that both the scope and irons are almost out of adjustment to the same location leads me to think there is a fitment issue.

I took it all down to clean and inspect and there are no signs of improper fitment wear or damage like burr's, dings, galling, wear marks etc. I do not have the tools anymore to check the receiver and barrel to see if they are concentric but I can feel side to side (L to R) play with the barrel hand tight. The barrel does not seem like it is pivoting side to side on the indexing pin like the receiver slot is too shallow but like the receiver was not machined flush.

This play feels like its about 4+ thousands or so kind of like a valve in a valve guide or piston gap etc. The play obviously goes away or takes a seat probably to the right or left when the barrel is torqued down.

I left a message with CMMG thinking maybe the receiver or barrel are not machined correctly but I was wondering if anyone else has had this happen or knows what the cause is and if it can be fixed.

[Erin]

my ar had a canted barrel. it caused sever marring of the caseings because the feed ramps were disaligned. the fix was a new upper reciver block.

[Sky_DiveR]

Sounds like you need to lap your receiver.

http://www.midwayusa.com/viewProduct/default.aspx?productNumber=810457

Edit: You also need lapping compound. I use the medium grit stuff from an auto supply store.

http://www.calguns.net/calgunforum/showthread.php?t=370584

[wintersborn]

I did not think to look at the brass specifically for this issue but I did not see anything odd about the brass that I handled. I did look at the feed ramp cuts to see if they lined up with the receiver and they looked ok but I imagine that kind of tolerance is hard to see.

I thought about hand lapping the receiver on a glass block but did not want to take the chance. The lapping tool looks like the way to go.

It makes sense that the receiver casting is the issue not the lathe turned barrel.

Is this common enough to warrant tools that fix this issue ?

I assumed that a Mil Spec receiver from a decent company (CMMG) would have been machined correctly. I also assumed that a factory assembled upper would be tested for proper fit not just function but such are assumptions : P

Should I ask for a new upper or have it sent in to be lapped/aligned ?

Thanks for the info.

[five.five-six]

AR15Barrel cant?

ar15barrels can fix it

[Sky_DiveR]

You'll occasionally run across a receiver that's not square. Depends on how many AR's you're gonna build, but it is simple and cheap enough to do yourself. If you don't want to do it yourself, give Seesm a PM. He does good work and is only about 30 minutes above Sac, in Auburn. He can square your receiver up in a lathe and probably be done within a few minutes.

[Milspec714]

where you located?

[hawaii five-0]

Does anyone have contact info for AR15 barrels?There website has no phone # listed.