timing barrel nut, what's the right approach here?

[riffraff]

Building my first rifle from scratch, a project I mentioned here prior just getting back around to it.. Basically a carry handle upper, spikes barrel w/ FSB - simple solid iron sight rifle is what I'm going for here..

Greased & worked in the threads, torqued, and the nut timing is just as wrong as it can be, as in it aligns right with about 20 lbs of torque and is about as wrong as it can be once you get to 30, is not budging enough to make a difference up to 75 lbs and I quit. Tried it a few times - no dice.

So I got some shims.. I thought it would be easy then in looking at this realized to me the best way is to put the shims between the barrel nut & barrel (not between the barrel & upper like I do see some methods employing via a cut in the shim).. Read up on it, seems although both practices are not uncommon the right way is probably remove the FSB, shim/time the nut, go back and re-install it..

Some of you guys here are really in the know w/ such things, do you agree? Any last words on FSB removal if so? Doesn't look too scary but man the stuff you read is all over the place on it.

Thanks in advance!

 

[burrhead]

Forget the shims. Take the nut off then grind, Dremel, or file off the tooth on the barrel nut that's in the way. I'm surprised that it indexes at 20# but doesn't before 75# but there it is.

 

[Scorch]

Put a shim on it. Typically, you can get the barrel nut to time up pretty easily, but if you're a little shy use the shim. Remember, adding a shim will move your barrel nut backwards. Shims go between the barrel nut and the barrel extension flange.

 

[riffraff]

Just to be clear, the problem with losing a tooth on the nut is then my hanguard will not time right either, since its indexed with the nut.

 

[riffraff]

And thanks for that guys, will try to torque again up to 80#, see if it budges.

 

[44 AMP]

Why so tight?

Of course, you're assembling (I don't call it building) an AR with new (non-GI) parts so I have no idea what's "right".

I can tell you that back in the 70s, when I was installing M16 barrels in an Army shop, the spec was "tighten to 35-40ft/lbs then tighten to align the nut for gas tube clearance"

So, I'm curious why that doesn't work now??

 

[stagpanther]

Been a while since I built/assembled/fumbled an AR with glacier guard, but I seem to recall that typically to get it timed right you'll be "tempted" by a looser torque or be forced to wail on that torque bar to spin up enough energy to get it timed to the next notch on the barrel nut. You mention it's your first build, so having good tools, vice etc is important to git her done. I've had run-of-the-mill armorer's tool that were inferior enough to cause real problems in getting the barrel nut torqued to higher pressures. Also, you might want to very carefully go over how you are fitting the parts together (definitely recommend against trying to remove or otherwise mess with the pinned front sight). Make sure your receiver and extension are thoroughly cleaned and degreased and then a good anti-seize lubricant is used. Takes a little sweat sometimes but should go together without any additional grinding/shimming/dynamiting etc. It'll work out.

 

[rickyrick]

You can also lap the receiver face, but that requires a tool that you probably don’t have either.
As long as you get it past 30lbs and the holes/notches line up, it will be fine. I don’t have any that it took me anywhere close to 80lbs. I have one with shims because the free float guard had to line up with the receiver perfectly.

 

[44caliberkid]

I use the torque to 35 - 40, then go as far as you have to to get the hole to line up. I've only had one require going to 80 ft/lbs, and boy, that was scary. I was expecting the receiver threads to strip any second. But it worked. Did you true the receiver face? You could have a burr or thick clump of finish there. If you don't have the tool, you can put some fine sandpaper on a piece of glass, and carefully work the receiver face just enough to remove the finish and leave a bright ring around the receiver face.

 

[riffraff]

Thanks Guys! I'm going to try to answer all your questions.

Am going to go back at it w/ 80 lbs available and see how that works but am not hopeful. Again, in short, it times perfectly around 20 (maybe a little more), then is out of time at 30 lbs and it does not come around to the next "slot" (at least at 75 lbs where I was when I tried it that way but maybe an 80 lb attempt will get it there)..

I do have the Aeroshell grease now but have been using STP Moly-EP, was avoiding anti-seize due to various opinions on the graphite it contains for this purpose..

Should also mention, as it is now I have a perfect surface on the feed ramps, anything I do between barrel & receiver is going to mess with that.

44amp - I am going so tight because I'm trying to get it aligned, at the min torque of 30 lbs it is just past a slot and it doesn't reach the next one at 75 lbs. Am operating a little scared, trying to do it right and not break stuff, so have not just let loose on it to force it to align..

stagpanther - the situation you describe w/ it being aligned at too light of torque and then requiring absurd torque is exactly where I'm at. Why do you not recommend sight removal - is it damaging by nature or hard to re-install after? Have a 6 inch vice, cheap model really, but holds fine, decent torque wrench that goes to 140 lbs or something (something I trust enough for engine rebuilding), armorers wrench and upper block are nothing special but do not seem to be holding me back one bit, easy enough to get a positive hold on the nut.

rickrick - I'm a little opposed to lap the receiver to make it work since that is just like shimming the receiver, although I am now going to inspect and true the surface as 44caliberkid describes

44caliberkid - thanks, going to try that, will know in about 10 seconds if it's got any burrs since they will shine immediately, but didn't notice anything funny, very nice looking upper

 

[stagpanther]

Why do you not recommend sight removal - is it damaging by nature or hard to re-install after? Have a 6 inch vice, cheap model really, but holds fine, decent torque wrench that goes to 140 lbs or something (something I trust enough for engine rebuilding), armorers wrench and upper block are nothing special but do not seem to be holdi

Just my opinion based on my experience: when you mess with that front site you're messing with the timing of two systems; the gas porting and the site alignment. All the YouTube "how to" videos make it seem like it's a piece of cake, it isn't unless you have experience, the right tools and know what to watch out for IMO. I've had a couple of barrels that received their final barrel treatment after the FSB was attached; that makes it even harder. I wonder if your upper's gas key pin slot might be contributing to the problem, if you have access to a another stripped upper (you might as well buy one, because you won't be satisfied with just one build once you've done one, trust me) I'd check the fit of your barrel to it and see if the tolerances are the same as your other receiver's. Something else to keep in mind--moving that extension back and forth (even by just one or two thousandths of an inch) within the receiver also might change the headspace tolerances, make sure your carrier/bolt will properly lock up with the extension's lugs. People say you don't need to check your headspace--I always do, even if the bolt and extension operate properly you may still have that "lemon" with overly long chamber--has happened to me more than once.

 

[FrankenMauser]

Lapping the receiver could help.
In my experience, it never hurts.
(And, unless you go full caveman, you won't remove enough material to affect function or alignment inside the upper receiver.)

Shimming is the best answer. As mentioned, the shim should go between the barrel nut and barrel extension.

If all else fails, find the combination of approaches that gets you closest to proper timing and proper torque, and then just crank it on over to the next slot/hole/castellation.


I also use STP Moly grease. You're not as alone there as you think.


Remember: Torque specs are for specific tools in specific orientations. Deviate from the specified orientation, or use a different tool for the job, and you need to recalculate the torque setting required to achieve the actual torque value.

 

[9x19]

(If stagpanther is correct) on your next build... I'd suggest using a barrel nut/hand-guard that requires no timing. The slim style nuts and hand guards are all I use these past several years. Oh, the joy!!

 

[riffraff]

Thanks again!

Stagpanther - what you describe is a concern, am used to PITA taper pins for things like aligning critical engine parts but looking at the fsb am a little squeamish about knowing I got it back together as well as it was initially too. Getting them out I think would be ok but in this rare case of removal then re-installation, maybe I will go to a pro.

I asked my favorite FFL about it today, who is primarily a shop with his own brand of high end ARs assembled by him on premise, told him was a little out of my comfort zone, and he is happy to take care of it and would remove the fsb and shim behind the nut if need be. Doesn't kill me on stuff either, so I think I will let him handle it and put my mind to a more straightforward project (maybe the re-barrel on this other rifle that has a set screw low pro block instead).

 

[riffraff]

Frankenmauser - thanks and I probably picked that grease from something you posted if you ever mentioned it, I read up on that subject a bit.

9x19 - yes for sure, most of my stuff is that way, anything other than pinned fsb would be a piece of cake really

 

[stagpanther]

I may have missed it--but why are you removing the fsb in the first place? My money is on your buddy will get it to work without "surgery."

 

[riffraff]

Stagpanther - 30 to 75 lbs does not result in correct timing (for gas tube but also 4 points on handguard).. other than if trueing fixes the problem (find out tonight), taking a risk of a full 80 lbs (which doesn't seem like it will), or there is an undetected defect present, the "most right" options seem to be a different nut or a shim placed between nut and barrel...

Now he may just be able to ream on it, but it would be with better tools and lots of experience (and if that's the end result it won't cost me much either).

 

[stagpanther]

Stagpanther - 30 to 75 lbs does not result in correct timing (for gas tube but also 4 points on handguard).. other than if trueing fixes the problem (find out tonight), taking a risk of a full 80 lbs (which doesn't seem like it will), or there is an undetected defect present, the "most right" options seem to be a different nut or a shim placed between nut and barrel...

If your buddy builds AR's--he'll know what to look for and maybe have comparable parts that he can compare the tolerances to. I fully get putting a carbine together that is reminiscent of a service rifle--but as others have said you'll find a free-float guard which has a barrel nut that does not need to be timed to the gas port makes things a lot easier.

 

[riffraff]

Stagpanther- oh definitely easier, kinda child's play actually. Don't like to give up after the excellent advice here but given it's something I may never deal with again on the FSB with an exactly wrong nut and expensive parts all around (spikes chf barrels and carry handle uppers just ain't the cheap stuff) just makes sense for me to let a pro do it right, I can fully assemble some other rifle that is without this gotcha...

This one basically I decided to assemble because in iron sights I really like the style upper and nobody really sells them in a carbine, or at least not any companies I have experience with.