Barrel install wiggle fix

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  • waccamawscout
    Bloodstained
    • Mar 2016
    • 60

    Barrel install wiggle fix

    Do you guys just use the barrel nut to attach the barrel or if you have a loose fit do you use a shim or some type of filling compound. On my last two builds I just used the barrel nut, but I had a tight fit. I have two new builds and the barrel has a little wiggle from the barrel extension to the upper receiver. For accuracy I want the tightest fit.
  • NugginFutz
    Chieftain
    • Aug 2013
    • 2622

    #2
    There are a few threads going right now about barrel bedding. In short, applying a bedding agent, such as LocTite Blue, is what has been recommended.

    For all those people who find it more convenient to bother you with their question rather than to Google it for themselves.
    If it's true that we are here to help others, then what exactly are the others here for?

    Comment

    • Lastrites
      Warrior
      • Apr 2017
      • 678

      #3
      Personally I would suggest shim stock if you have a loose wiggly fit.

      Comment

      • Slappy
        Warrior
        • Feb 2014
        • 711

        #4
        I would get/use different uppers?? That is just an opinion, there are way to many good/better uppers that do not require shims these days and have a very good fit and finish. BANG BANG!!

        Comment

        • just_john
          Chieftain
          • Sep 2012
          • 1565

          #5
          You can't tighten the barrel nut enough to mitigate impulse vibration at ignition. If there is ANY slack between the barrel extension and the upper there will be some motion. Putting in shim stock may help for a while but if it is anything except steel or aluminum and if it gets damp then electrolysis will soon eat up the upper. Loctite is a lot cheaper, easier to form ( it just pours in ) and is inert so there is no chemical reaction with either steel or aluminum. And it works!

          Comment

          • LRRPF52
            Super Moderator
            • Sep 2014
            • 8569

            #6
            The AMU noticed the problem of barrel flex inside the receiver down at a match in Australia back in the 1980s IIRC. Sling tension would pull shots if it wasn't consistent, so they came up with the concealed free-float tube and started bedding extensions into the uppers, after the uppers were trued up.

            One of the approaches used was to take stainless sheet stock of the correct thickness to compensate for the diametric difference between the OD of the barrel extension and the ID of the extension tunnel in the upper. They would wrap the extension and test-fit, then apply bedding compound and seat the barrel in using high torque in final assembly.

            The next step was to order undersized and trued, squared, and customized A2 uppers with custom extensions that wouldn't even press fit. They would thermo-fit the two like a Steyr SSG barrel, heating up the upper after freezing the barrel. With the 2 parts in opposite thermal conditions, you quickly snap them together then let them equalize at ambient temperature, and you have an extremely unitized barreled action.

            The challenge with this approach is controlling uniformity in your anodizing to get that thermo-fit in a production scale, but all methods aim to basically unitize the barrel and action.

            Combined with a trued-up bolt face and lugs, and a bunch of other tweaks to the design for more smooth handling of brass, and you can have a really fine-tuned system that is extremely easy for armorers to work on compared to the M14.
            NRA Basic, Pistol, Rifle, Shotgun, RSO

            CCW, CQM, DM, Long Range Rifle Instructor

            6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

            www.AR15buildbox.com

            Comment

            • waccamawscout
              Bloodstained
              • Mar 2016
              • 60

              #7
              Yeah, I have 3 barrels and 2 forged uppers and 1 billet upper and a little play in all of them

              Comment

              • waccamawscout
                Bloodstained
                • Mar 2016
                • 60

                #8
                Thanks for the advice. I feel it maybe the best to use the as shim. If I use loctite which is best

                Comment

                • NugginFutz
                  Chieftain
                  • Aug 2013
                  • 2622

                  #9
                  I can't speak to other types, but LocTite Blue is the most commonly reported. I've used it on two different uppers to great effect. Both rifles are sub moa shooters. One is a 5.56 blaster, the other a 22" bull barreled Grr. I've not yet needed to remove either barrel, but forwarned is forearmed. I'm prepared to use a hairdryer/heatgun to warm the LTB prior to disassembly, whenever the time comes.
                  If it's true that we are here to help others, then what exactly are the others here for?

                  Comment

                  • LRRPF52
                    Super Moderator
                    • Sep 2014
                    • 8569

                    #10
                    You can also use MarineTex, which has the least shrinkage after curing according to one of the big bolt gun guys who does bedding and measured several of the different options they use for pillar and glass-bedded stocks.

                    I like to parts-select my uppers for ones that have the tightest fit between the extension and the ID of the tunnel in the upper.

                    I have also tried building up Cerakote in the tunnel for the extension, then bedding the barrel in there, which works too.

                    ID of the tunnel is not supposed to exceed 1.000", -.0007 allowable. The barrel extension OD is not supposed to be smaller than .9980. Can be .9995".

                    Some precision-minded shops will spec .9997" OD extensions and .9993" ID tunnels, and thermo-fit them with heat on the upper and freezing the barrel, then pull the barrel out of the freezer and insert it as soon as the heat gun comes off the upper.

                    Biggest challenge from a manufacturing perspective there is controlling your anodizing dims part-to-part to the 4th decimal. Easier said than done.
                    Last edited by LRRPF52; 08-26-2017, 02:13 AM.
                    NRA Basic, Pistol, Rifle, Shotgun, RSO

                    CCW, CQM, DM, Long Range Rifle Instructor

                    6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

                    www.AR15buildbox.com

                    Comment

                    • sneaky one
                      Chieftain
                      • Mar 2011
                      • 3077

                      #11
                      Nuggin,
                      Bill A. used Kroil to separate if loctited on. Heat gun can ruin the temper of the upper receiver.


                      When using Loctite, get the surface intolerant stuff 243- Permatex is 24300? It's all I use. on 2 builds, The last 2--- I used 1 - 2.0 oz. bottle. BFT's was 1 . Both shoot great.

                      I used marine tex years ago on my fishing boat-hit a rock small tear in aluminum bottom - worked great. It can be drilled and tapped-it is that good.

                      Probably near impossible to undue the bbl. once it dries. Get a low budget upper rec., have the front squared- meld it together with marine tex- toss it all when accuracy goes away.

                      That would be option B for me.
                      Last edited by sneaky one; 08-29-2017, 12:08 AM.

                      Comment

                      • Kswhitetails
                        Chieftain
                        • Oct 2016
                        • 1914

                        #12
                        I am the new guy here, so take this first line as a disclaimer. I have used threadlocker my whole life though, and have used it for similar purpose on hydraulic fittings and fire water pipes and valves. It is basically an anaerobic epoxy that fills the gap between the thread spaces in a torqued fastener to prevent vibration creep, basically making the union a solid connection - like a weld. Functioning to do EXACTLY what we're wanting here, and only as far as needed.

                        I did some research last time we covered this, and decided to bed my own. I trued the upper's face, which actually was pretty far off. Wheeler tool I believe. I cleaned the upper of lapping compound and oil, then used a thin coat of Rem-oil on the contact surfaces of the barrel and upper.

                        I use a squeeze bottle of Permatex blue #24300. It has a gelled consistency, is oil and fuel/solvent resistant, and cures in oiled environments. This means that you can lightly oil your upper interrior, the outer surface of the barrel extension, grease your threads, and not negatively effect the blue. You just wipe the excess off that smashes out onto the threads with an alcohol wipe, or other solvent cloth. Then grease and install the nut and hand tighten until there is no more wiggle in the barrel. Leave it for 6 hours. By not overtightening, if there is any excess locker residue on the threads, it comes off easily. Clean your threads inside and out, THEN you can replace the barrel nut and proceed to tighten to torque spec.

                        I used that process with a side charging upper, and the next day decided I didn't like to side charge after all, and decided someone else needed the thing more than I.

                        Surprise, it came apart! But I had to use my Brownells upper reciever clamp insert (the thing that goes into the interior of an upper when you clamp it in your vise) as a dowel to drive it out of the upper. The fit was perfect, absolutely no space between the two pieces. The Permatex that was left was obviously heavier on one side than the other, indicating that the extension was a sloppy fit inside the uppers carrier tunnel. It also flaked off with my fingernail, and came off in larger flakes, it was easy to remove. Probably because of the Rem-oil I used before assembly. I was surprised how effective the Permatex had bedded the barrel to the upper. It was definitely worth the effort and worry. I'll never worry about doing it, and will most assuredly do it in the future on all my builds.

                        Is it necessary? Probably not. It does definitely do something toward mating the barrel with and "unitizing" the fit between the two. Thus and by definition, is therefore a better-than-not step in any upper build.
                        Nothing kills the incentive of men faster than a healthy sense of entitlement. Nothing kills entitlement faster than a healthy sense of achievement.

                        Comment

                        • sneaky one
                          Chieftain
                          • Mar 2011
                          • 3077

                          #13
                          Read back aways, KsW, read back...

                          Comment

                          • StoneHendge
                            Chieftain
                            • May 2016
                            • 2009

                            #14
                            To add to the list of bedding options, I finished up a 6.5 AR10 over the weekend (yes, I'm now also one of THOSE guys. Now I get comments like "I want to get one of those - that's cool - what brand is that?" and "hey, Bobby, check it out - he's shooting a crEEdmoor").

                            Put a Proof Research CF barrel on it and when I was on the phone with them asking questions, Mike made sure he went over how they recommend bedding: 1) tight enough to need a heat gun to get it in? Awesome! 2) takes a little effort to get it in.? Green loctite. This is the penetrating stuff. The rational is that it will seek gaps and provide a little fill in those areas. 3) slips right in and maybe even has a bit of play.? Stop by the auto parts store and pick up some Permatex Indian Head Gasket Shellac.

                            Well, my barrel slipped right in like the receiver was a five dollar whore. Did a little research and saw the gasket shellac was made for applications up to 350 degrees. I thought: will I be able to get it out if there's a problem with the barrel? I decided if there was a problem and I couldn't get it out, they were getting the receiver along with the barrel since it was their recommendation! Going with their recommendation for bedding could obviously also speed up any process if there was a barrel problem. My local auto parts store didn't have the Permatex but Karl assured me that the Versachem Lion Gasket Shellac was essentially the same ("it just has a Lions Head on the bottle instead of an Indian Head"). It's about as thick as molasses and I spread it evenly on both the extension and inside of the receiver with a flat quarter inch wide watercolor brush). Let it stand a couple of minutes per the instructions and it took quite a bit of effort to get it in. Didn't see any evidence of seepage on the barrel nut as I went through the torque & unscrew process, nor on the chamber side.

                            So far so good. I'm certainly not going to have to send the barrel back and as far as I can tell shooting some factory ammo to liberate brass, it looks like it should be at least a 1/2 MOA shooter on the rare occasions that I'm a 1/2 MOA shooter.

                            Just figured I'd throw this into the mix given where the recommendation came from.
                            Let's go Brandon!

                            Comment

                            • waccamawscout
                              Bloodstained
                              • Mar 2016
                              • 60

                              #15
                              This is why I love this place. Thanks for all your help. You guys have always been helpful.

                              Comment

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