Over-torqued upper receiver, and best way to unassemble...

[CLP]

Built a 6.8 SPC with a WOA 16" SPC II Stainless barrel and their upper. I put a Yankee Hill free float handguard on it. Fun rifle and it shoots fine. However, I've got a perfectionist streak in me and I can't let something go. I assembled it using a clam shell-type vise block. I used a torque wrench to install the nut in increments of 10lbs on the torque wrench until the scallop was aligned with the gas tube hole of the receiver. While checking for the alignment, I would have to remove the part of the vise block that occupies the interior of the receiver. Well, at least on one of the 10lb interval of torquing the barrel nut I left it out. Visually, it looks flawless.

Now, to zeroing in... Set a SR-1 reduced target at 100yds. Mounted an Eotech XPS2- the instructions stated that only a minimal amount of adjustment would be necessary. I wasn't even on paper. I would estimate I was at least 18" to the right of the X ring. No significant elevation issue. The Eotech has since kept zero. Next, I installed a set of magpul buis. Same thing as above. I'm wondering if I bent the receiver somehow. Is that possible and would it cause that lateral deviation I've described?

Finally, I have another receiver I would like to install this barrel in. What's the best way to clean out the old Loctite I used on the barrel nut (where the float tube mounts)?

Thanks for your input!

 

[rcmodel]

Set a SR-1 reduced target at 100yds. Mounted an Eotech XPS2- the instructions stated that only a minimal amount of adjustment would be necessary. I wasn't even on paper. I would estimate I was at least 18" to the right of the X ring.

Eotech mislead you, sort of.
Only 18" off at 100 is a "minimal adjustment"!

Put a new optic or BUS on any flat-top and I would be amazed if it was on paper at 50 yards, let alone 100 yards.

I always bore sight at 10 yards using the EoTech bore sight target to get close enough to extend the range and fine tune the zero.
http://www.eotech-inc.com/documents/M16A4-M4MWS_EOTech_LBS_Target.pdf



I'd use a heat gun or propane torch to "smoke" the old lock tight.
Once you do that you can clean it off with a bronze bore brush or something.

rc

 

[BBBBill]

The allowable torque range is quite broad for ARs and they do not require a whole lot to secure the barrel more than adequately. Just curious. How much did you torque it?

 

[CLP]

I was within the normal torque range at 60lbs. My concern was that on at least one (I think twice though) of the turns of the torque wrench that the vise block insert wasn't in the receiver. That amount was the minimum it took to align the scalloped portion of the nut.

RC, what exactly do you mean? Should I use heat gun to heat up the barrel nut/receiver?

 

[rcmodel]

Yes.

rc

 

[rbernie]

If the receiver somehow bent at all (and I'd love to see how a 7075 T-6 receiver could bend instead of cracking), I would expect to see abnormal wear in the bolt raceway within the receiver. If you're not seeing dramatic and asymmetric wear to the anodizing inside the receiver, then you can assume that something else is wrong and that the receiver itself is likely just fine.

Is your front sight pinned, gas block mounted, or forearm rail mounted?

 

[CLP]

No abnormal wear as of yet. The front sight is rail mounted (low profile gas block). If the buis were alone in being deviated so far to the right then I would assume it was the free float guards at fault. But, it's also the EoTech which is mounted on the receiver. And the deviation (if that's even the right word to be using) is approximately the same between the two of them.

Regarding the heat gun (I was unable to pose my question since I was at work earlier), how long should I use it? Is there a particular temp I'm shooting for? Heh, no pun intended... Am I to expect the heat to cause the receiver to flex a bit in some way and better seat the barrel?

 

[ljnowell]

If what I am reading is right, and you are saying that the sights out of the box, when installed on the gun, we only 18 inches to one side at 100 yards, then I would say its probably not a problem. Maybe thats just me, I dunno. I own some ARs, have worked on them, but never installed a barrell.

 

[dprice3844444]

you don't need locktite on the barrel nut because the gas tube keeps it from moving.use an antiseize grease with out graphite

 

[rbernie]

If the buis were alone in being deviated so far to the right then I would assume it was the free float guards at fault. But, it's also the EoTech which is mounted on the receiver. And the deviation (if that's even the right word to be using) is approximately the same between the two of them.

You may have a co-incident issue with the gas block being canted and the mount for the EOTech being weirdly. Do you have the same offset issues with the EOTech mounted on the rail section at the front of the receiver vice the back of the receiver?

Regarding the heat gun (I was unable to pose my question since I was at work earlier), how long should I use it? Is there a particular temp I'm shooting for? Heh, no pun intended... Am I to expect the heat to cause the receiver to flex a bit in some way and better seat the barrel?

The reference to heat was specific to your question about how to remove locktite. If you used red locktite, you will need to see it smoke before you can get it to release. If you used blue or purple locktite, then you should have to do nothing special (no heat - just torque) to get it to release, and do not need to do much of anything other than brushing to reassemble things.

 

[CLP]

The loctite was on the outside threads of the barrel nut to help stabilize the YHM FF handguard. It's blue loctite, and I guess I should have been more specific in that I wanted to know if there was a solvent that would help wipe out the old loctite from the threads when I prepared to reinstall it.

The aperture on the rear sight has to be adjusted way off center to zero the rifle. I don't see this problem with factory assembled rifles, so I did something wrong. I have to figure it out and install everything properly.

 

[rbernie]

I suspect that the gas block is not centered. It helps to snap a line down the centerline of the barrel from the locating pin past the gas port, so you can use that as a reference.

 

[ljnowell]

The aperture on the rear sight has to be adjusted way off center to zero the rifle. I don't see this problem with factory assembled rifles, so I did something wrong. I have to figure it out and install everything properly.

Gotcha.

 

[CLP]

I suspect that the gas block is not centered. It helps to snap a line down the centerline of the barrel from the locating pin past the gas port, so you can use that as a reference.

Like using a chalk line... That's a good idea. I just eyed it. I suppose it would be simpler to start with fooling around with the gas block first. I didn't consider it before because I didn't feel the bolt carrier key catching and there didn't appear to be any abnormal wear on either the inside of the carrier key or the end of the gas tube that it mates with. However, I can easily see how the block might have canted a bit when I torqued it down (clamp on style block)