New build and installing an MI-SSK proprietary barrel nut. Started with a torque value of 30 ft lbs and the index is just past alignment so gas tube won't go in. Unloosened barrel nut and tried 35, then 45 and I can see going to 60 isn't going to get it aligned. Don't want to do any damage and thought I better come ask the pro's how to proceed. Took the barrel nut completely off a few times and re-installed with the same results (hoping it would index a little farther each time. Doesn't look like that is going to make. I see you can purchase a lapping tool from Brownells, but thought I would check other options first.  Thanks for any suggestions.

Tec

Use the correct grease, and torque it several times.

You need to back off the nut each time, to re-torque

barrel-nut-shim-kit

Please don't purchase THAT tool from Brownell's. If your upper is new (was never barreled), that nut will align if the upper is fixtured correctly, your using grease (threads and front side of barrel extension flange) and you have properly pre-stressed the the threads.

No purchase of the Brownell tool. I did send away for some shims through Amazon (.32mm each shim = .012"). I am using the Geissele reaction rod to hold the receiver (barrel and receiver are both new and never mounted).  Tried 10 times mounting the barrel to receiver up to 50 Ft lbs and I can see going to 60 is just not going to get the nut far enough to allow the gas tube entry into the receiver.

Pulled it all apart and placed into the safe.  Waiting for some shims. Don't know what else to try. By pre-stressing the thread, do you mean to tighten the nut at a specific torque and leave it there a bit

This

Tightening the loosening 3 times regardless of whether the gas tube will index or not. You may need to pre-stress up to the 80 pound max.

Center-to-center the notches on the barrel nut are 18 degrees apart or .003 of an inch of rotational distance. One shim will move the nut 4 notches to the same location. It will be interesting to see how many shims it takes to time it.

Have the same barrel nut on my pistol. Ended up torquing it to about 80 to get it to line up after following the proper procedure for torquing with proper grease.

Lap the face of receiver.  It takes two seconds.  The kit is at brownells. If you plan to build uppers, its worth getting the tool.  If not, use it this once then sell it on the EE

Wheeler makes one too....  I haven't bought or tried it yet, but the flexible drive shaft seems to be a good design feature to minimize binding.

I have to lap at least one of my builds. As the barrel heats up, the POI walks to the right and then returns when the barrel cools. Hope this corrects the issue.

The lapping tools work fine,use by hand and with very little work the nut will index at min. tourque

Alright, I am at a loss. I purchased the shim kit from Amazon and it was a kit with 5 shims that were supposed to be .32mm or .0126" each. However, I measured the shims and they were .50mm or .0197".  Started with one shim and then torqued the nut to 30 ft lbs. No alignment from 30 up to 60 ft lbs. Then tried it with 2 shims and went from 30 up to 60 again and no alignment. Then went to 3 shims (~.060") from 30 to 60 ft lbs and no alignment. Finally with the 4th shim in place, I got it timed at 60 ft lbs.  Then tried placing the MI-SSK on to check the fit and I have a gap between the upper receiver rail and the SSK rail, I guess equivalent to the shim space (or there abouts).

I can't live with that. It was probably a dumb move to get this shim kit instead of going with the kit at Spikes tactical

Spike’s Tactical Barrel Alignment Kit
3 Thin Barrel Nut Shims (.0015" Thick)
3 Thick Barrel Nut Shims (.003" Thick)
1 Thin SAR Barrel Nut Shim
1 Thick SAR Barrel Nut Shim

Didn't care for the shipping costs of $12.78 for a shim kit that costs $11.95.

So, I've put the build away until I figure what to do next.  Do I eat it and go with the Spikes kit, or do I get the Brownells lapping tool. I do plan to do other builds, and might be ahead if I bought the lapping tool however I am concerned about the statement CAC01. What;s the downside to lapping the receiver?

More comments please.

If you wanna play, you gotta pay.

I had no trouble with my SSK, guess I was lucky.
Sounds like lapping may be your only (and best) choice.

I would use the lapping tool, before I would shim my barrel, just like my opinion, man.

Great, thanks for the input. I have ordered the Wheeler lapping tool. I'll lap it and once I get it timed, I'll report back.

Thanks again,

Tec

Mary, Mother of Jesus... That fixture is off the hook.

Get another barrel nut to have on hand.

I was in a similar situation After about 10 - 15 attempts it would not line up properly. Ended up doing a light clean up of the threads on the nut and receiver with a brass bristle brush, applied proper lubricant, and tightened it up again and it worked.



Not sure what made the difference but was just glad it went together that time.

Got the Wheeler AR-15 Receiver Lapping Tool in today. Damn thing is made in China. Not happy about that at all, but will give it a go later this week.  First I think I will try cleaning the thread with the brass bristle brush on the barrel nut and receiver threads.  Then if no go, on to the lapping.

Tec

Yes, I have the Moly grease.

MI sent me a new barrel nut. I gave that a go and it also would not line up, through many many tries. Must be in the receiver. I took the lapping tool and figured it was time to give it a try. lubed the tool up and checked the action in the receiver.  Turned smooth as butter. Placed the grit on the tool and chucked it up to the cordless drill and gave it a spin for 30 second with very light pressure pressing into the receiver. Removed the tool, cleaned every thing up. Applied a little more moly to the threads and started the install. 30 lbs not lined up, but looking much better than before. At 55 ft lbs, dead nuts on, perfect. So I am happy.

I have got to state my surprise over MI's customer service. I never contacted them about this issue. Andy was browsing threads and came across my thread. He contacted me and offered a few suggestions, and offered to send me a new barrel nut before I spent any more money trying to get it together.  Andy, thanks so much for your help and assistance, and the barrel nut. It didn't work, but no fault of MI. It feels pretty good to see how support from MI is offered without being requested. Big Kudos from me, and should be noted for others. I love the hand guard, and plan to use other lengths on different builds.  I'm willing to send the 2nd barrel nut back on my dime if it can be used by MI. If not, it's always good to have a spare.  Again, thanks much to everyone for your help. bottom line, we got it working and I'm happy with the outcome.

Thanks,

Tec