Barrel install wiggle fix

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  • Klem
    Chieftain
    • Aug 2013
    • 3507

    #31
    Originally posted by Kswhitetails View Post
    I haven't been back here in a while. Sorry Klem, I missed your question, so here I go.

    In that particular upper receiver, it had already been well loved prior to the mating of this barrel extension. The reason there was more bedding material on one side than the other was a matter of previous wear. ( I believe, all things being equal.) The bedding material did it's job, took the play out of the joint, and the rifle produced much better precision.

    IF the face of the receiver is square, and IF the tunnel is true, and IF the extension face is square to the bore, the extra material on one side over the other is a good sign; the empty spaces in the union allowing movement have been removed. The barrel nut, properly torqued, WILL square the extension to the face of the receiver, assuming that the faces of both pieces are clean and no material is "shimming" the two apart, and that the aforementioned "ifs" are met.

    In all actuality, it takes a true set of gauges and tools, not found in most garages, to determine if all of the above "IFs" are true. The bore of the upper being true to the bore of the barrel is the key. You want the bolt to be square to the chamber face and extension lugs at the last moment of lockup and the first moment of release. If the bolt wear wasn't an issue in non-true assembled uppers, the square of the setup wouldn't reallly be an issue at all, we would all just adjust our sights for bullet impact and move forward then being blissfully ignorant of the out-of-square condition. Precision in rifles is about repeat-ability, rather than being "square". The purpose of using bedding material in this case is to allow the shot to be repeated by removing the movement variable of the or "slop" between the barrel extension and upper.

    SO:

    The squaring of the receiver face is to lessen or prevent the bolt wear on lockup and unlock, and has nothing to do with precision; As well as to make the overall BCG travel smoother and more reliable. Bedding the barrel removes any possibility of movement between the extension and receiver, making repeated predictable bullet impact a reality.

    IF you do not see any unusual bolt lug wear, squaring your receiver is unlikely to by itself correct any accuracy issue. IF you cannot pull the barrel from the upper receiver by hand without bedding it, then it is unlikely that bedding the extension will increase accuracy.

    IF you wish to know rather than guess, then square the receiver, and bed the barrel. Both processes are easily accomplished and both are always absolute in their removal of these two variables in the precision factor of any particular rifle.
    KS,
    Thanks for replying

    Picturing what you are saying in my head I can only see a squared upper still being out of alignment and needing more glue on one side than the other if the nose of the upper is out of alignment with the upper itself (scenario 2 in the diagram). i.e. the bore of the upper is out of alignment with the bore of the nose. In that case how do you know which direction to bias the barrel to align the axes when you put it all together?



    Note scenario 2 in the diagram the nose is closer to side A than B, a manufacturing fault. If however you make the mistake of biasing a random side on a perfectly true upper then you just end up with parallel axes, Scenario 1. Parallel axes, while not perfect is still more preferable to an untrued nose (Scenario 3), where the upper axis is at an angle to the barrel. And if you end up accidentally putting more glue at 12 or 6 O'clock then the elevation knob on the scope makes it a non-issue.
    Last edited by Klem; 01-19-2018, 03:49 AM.

    Comment

    • Kswhitetails
      Chieftain
      • Oct 2016
      • 1914

      #32
      The answer is in short that I guess you wouldn't. I am imagining a scenario wherein the overall out of axis is within the usual suspects of acceptable accuracy for (input the intended rifle's purpose here). If someone finds that they cannot zero a rife at 600 meters, this becomes academic anyway and will be looking into further time and money to accomplish their goals. I can't foresee though, anyone actually finding a situation where they couldn't find acceptable accuracy at a given range if acceptable precision is achieved first. This has always been the process, we get the bullets making small consistent groups, then we move our sights for the "zero".

      The image you post is educational in its illustration of the issue, but in reality the tenths of a degree we're discussing are hardly noticeable within 600 yards, and at that point I'd assume (here we go again) that folks that are interested in shooting their AR at that range consistently spend far more money and time than those who would be willing to settle for a receiver that showed up badly out of round/square/true, etc... Again, just my assumption.

      The other issues I see arising are an upper bore being off-center. Now this, is a total failure and should never be acceptable, regardless of squaring the face of the receiver or not. This would be readily apparent after just a few rounds, with the BCG making ugly sounds and scoring the inside of the carrier bore in a non-symmetric way. I've personally never heard of a case that bad, though I am sure they have arisen.

      In the tolerances inherent in the AR system as far as BCG travel, bot lockup, and extension capture (assuming the barrel is torqued correctly), I can't imagine someone being able to assemble the parts, and have the BCG operate freely by hand if they are off by very much at all. The system itself eliminates the bad apples by requiring a fairly square/true relationship.

      For me - bedding the extension into the upper means you're using a flowing strata that hardens in place after the two pieces are mated together. Torquing the barrel extension into the receiver imparts pressures that hydraulically force the bedding strata to find the voids. Since the barrel nut will force the two axes together within a very minute measurement, the danger of the two being far enough out of square with each other to cause real problems is minimal. (Which is why AR bolts breaking due to uneven mating with the extension are rare in the overall scheme of things, even with thousands upon thousands of these things being built in garages every year)... The bedding strata will seek it's own level - and when the two pieces are separated, you will be able to see just how much room there was between the extension and the inner race of the receiver, even a tiny thousandth is obvious. What I am getting at is that the spaces we're filling don't represent enough of a void to make the scenarios in the pictures you posted occur, and if they were, we would be replacing parts rather than bedding them. (assumptions abound!)

      Am I assuming incorrectly? (I assure you, this would be the very FIRST time...)
      Last edited by Kswhitetails; 01-19-2018, 04:28 AM.
      Nothing kills the incentive of men faster than a healthy sense of entitlement. Nothing kills entitlement faster than a healthy sense of achievement.

      Comment

      • Klem
        Chieftain
        • Aug 2013
        • 3507

        #33
        I have grossly exaggerated the angles and offset in my diagram to make it clear what I am referring to. Scenario 3 being a crazy, unrealistic angle I thought would communicate that.

        Comment

        • Tex Nomex
          Warrior
          • Dec 2017
          • 185

          #34
          My thoughts and opinions:

          A bolt has some play in the bolt carrier.
          A carrier has some play inside its upper receiver bore.
          A barrel extension may have some lateral play when placed inside the upper receiver's threaded extension.
          A barrel extension pin may have some rotational play in the upper receiver's pin slot, allowing rotational barrel play.

          Lapping the receiver removes flashing/coating imperfections from the receiver's mating surface and trues that surface with the carrier bore. This is good for limiting uneven wear of the bolt lugs. But, more important to one's sanity, it makes receiver-mounted sights and scopes more parallel to the barrel bore.

          This does assume the receiver's threaded extension is in alignment with its carrier bore. You could check this by measuring runout at various places along a straight line thru the center of the entire receiver up thru the threaded extension bore. I, for one, would find such a test among receivers from different manufacturers of great interest, just to see the variance.

          Bedding the barrel extension mitigates rotational spin and lateral movement of the barrel extension. It probably won't ensure that the barrel extension is centered perfectly within the receiver extension bore. The person installing the barrel would be responsible for making that happen, however such a thing is done. But the amount it could possibly be off is very small and the effect on performance real-world performance is probably negligible.

          Philosophy:
          When you purchase a pre-built upper, you are counting on the builders to take care of these things for you. If the builder makes and its own parts, they can tweak their components to minimize the play between components. Or, having hundreds of receivers and barrels to choose from, they can mix and match their parts to achieve the same results. But you pay for that with the premium price tag and must accept the corresponding lack of component choices.

          The military probably doesn't give a rip about a little extension pin play. Parts within spec get assembled.
          Premium outfits might care more about fit and they should. They are getting BIG $$$$ to care.

          In an effort to destroy my credibility completely, I admit to having used PermaTex Indian Head Gasket Shellac Compound to bed more than one barrel in the last 3 years. Those guns are trouble-free and shoot well. I haven't taken one apart yet, so I can't yet speak to the effort needed for disassembly. Has the potential to suck mightily.

          As to barrel tightness in a receiver extension: Barrel extensions have as much to do with it as the receiver. On average, barrels with shiny extensions seem to have more play. If you think it's sloppy and that means the barrel-maker sucks, does Cerakoting the extension make it all better? Just saying...

          I also use synthetic+moly grease on the receiver barrel extension and buffer tube extension threads. I keep the torque on the low half of the specs. It works.

          In fact, if you don't use some sort of lube on the threads, "hand-tightening" the barrel nut isn't really tightening it when using the Indian Head method of bedding and the barrel will pop up out of place during curing. .

          Just my $0.02. Your reality may differ.

          In the end, if someone wants absolute accuracy, they don't shoot semi-auto. So worrying much about the squareness of the sides of threaded extension to the upper itself on a late model name brand upper receiver? For once, Hudson's got it right...

          HudsonAsksWhy.jpg

          Nomex: ON
          "The best we can hope for concerning the people at large is that they be properly armed."
          -- Alexander Hamilton, The Federalist Papers at 184-188

          Comment

          • Kswhitetails
            Chieftain
            • Oct 2016
            • 1914

            #35
            Klem: Understood, my apologies if I came across as too hard on the diagram. For illustrations sake, perfect effect.

            Tex, You are correct in all cases. The bedding process has as its singular purpose to remove any possible movement in the union of the barrel extension to the upper during the stresses incurred during firing. Lapping the receiver means to remove enough material from the face of the receiver to allow solid contact with the extension at as close to a perfect 90degrees as possible. In theory, doing both would make a monolithic junction between barrel extension and receiver at a perfectly true, square angle.

            Your comment about the pursuit of absolute accuracy is what I was hinting at above. If someone is seeking precision beyond the capabilities of the AR platform, due to the innate "slop" in the carrier and bolt system, then they do indeed need to quest into bolt actions, or break action, or rolling block, as these all have inherently tighter tolerances with a round chambered and bolt locked. I guess this is a flaw only in purpose and design, rather than components. However, the Grendel really doesn't have the reach to get out to the ranges where the tiny tolerances in a properly assembled BCG system begin to make a large effect. I know folks shoot their Grendel at 1500 yards, but how many out of a thousand even have access to a place to do so? And of those, how many actually do regularly? And of those, how many are using the less hot-rod-able AR over the bolt guns?

            BUUUUT - for those of us that haven't matured to the bolt action Grendel yet... the pursuit continues!
            Nothing kills the incentive of men faster than a healthy sense of entitlement. Nothing kills entitlement faster than a healthy sense of achievement.

            Comment

            • Keef
              Warrior
              • Jun 2017
              • 296

              #36
              I started truing them after getting a radical complete upper that would only zero with the rear sight almost maxed out to the right. After cleaning up the face with truing tool rear sight was centered. Maybe none of this matters but I really didnt like being one click from maxed out. Please dont ask me what i bedded extension with......

              Comment

              • BluntForceTrauma
                Administrator
                • Feb 2011
                • 3897

                #37
                Uh . . . what did you bed the extension with? Chewing gum?
                :: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets

                :: I Drank the Water :: Revelation 21:6 ::

                Comment

                • Keef
                  Warrior
                  • Jun 2017
                  • 296

                  #38
                  Good old JB weld. Cleaned the extension with acetone and lubed the upper with kroil oil, greased threads and nut. Mixed it, smeared thin layer on the extension and inserted carefully. Make sure none gets in the threads.

                  I torqued it let it dry over night. Next day went back to vice and unbolted barrel nut. Barrel wouldn't budge or wiggle by hand, so I crossed my fingers grabbed a wooden dowel and gave the extension a smack or two. Ah ha! now I see movement. Everything worked as planned the jb bonded and stayed on the extension and released from upper. The barrel is a beotch to get in and out but once its in it doesn't move!

                  I wouldn't say it's for the faint of heart and I understand if I lose all credibility...... but it's strong won't melt out.

                  Comment

                  • Keef
                    Warrior
                    • Jun 2017
                    • 296

                    #39
                    Home alone this weekend so I didn't get the stink eye for pulling the tool bag out. Lol.
                    Just took it apart for the third time and it took a wooden down and mallet to make it happen. Here are the pics it's a super thin layer but it makes a big difference.
                    IMG_20180119_233449-1125x1500.jpg

                    IMG_20180119_233513-1125x1500.jpg
                    According some bolt action rifle bedders it has less thermal expansion/contractions than some much more expensive products. But I don't really know.

                    Upper face after truing. You can see much more material was removed from one side.
                    IMG_20180119_234948-1125x1500.jpg
                    Last edited by Keef; 01-20-2018, 03:51 AM.

                    Comment

                    • Klem
                      Chieftain
                      • Aug 2013
                      • 3507

                      #40
                      Originally posted by Keef View Post
                      Good old JB weld. Cleaned the extension with acetone and lubed the upper with kroil oil, greased threads and nut. Mixed it, smeared thin layer on the extension and inserted carefully. Make sure none gets in the threads.

                      I torqued it let it dry over night. Next day went back to vice and unbolted barrel nut. Barrel wouldn't budge or wiggle by hand, so I crossed my fingers grabbed a wooden dowel and gave the extension a smack or two. Ah ha! now I see movement. Everything worked as planned the jb bonded and stayed on the extension and released from upper. The barrel is a beotch to get in and out but once its in it doesn't move!

                      I wouldn't say it's for the faint of heart and I understand if I lose all credibility...... but it's strong won't melt out.
                      Keef,

                      You are the first to say they used two-part epoxy. This makes sense to me as it's a stronger glue.

                      What's the brand of upper in your photo?

                      Comment

                      • Keef
                        Warrior
                        • Jun 2017
                        • 296

                        #41
                        Came with a complete Radical upper from Atlantic Firearms. Not sure if they actually make the uppers or not though. I don't think there is any branding marks on it.

                        Comment

                        • sschefer
                          Bloodstained
                          • Jan 2018
                          • 26

                          #42
                          5.56 long range.jpg
                          I just finished, like 10 minutes ago, putting a Bishop comp 5.56 barrel on a VLTOR upper. My lapping bar fit pretty tight so I lapped the face and the entire upper internally with 800 grit lapping compound. I did it vertically and I did use the drill because there was zero side play in my bar. I checked the receiver top for square to the front with my machinist square and it was dead on the money. When I was done and had the upper washed and dried I put my reaction bar in and inserted the barrel which fit snug with zero detectable play. I checked the ramps and could feel a very slight ridge so I shimmed the inside edge of the barrel extension with a .001 shim and that took care of that. I did follow up by polishing the ramps and I still think it's a little odd that that .001 shim fixed the barely noticeable ridge. By the way, if you shim the receiver side of the barrel extension, you have to cut the shim to fit around the indexing pin. I'm using a Noveske barrel nut and it took another .008 in shims to get it perfect at 60 ft. lbs. of torque.
                          I did a ton of checks and the barrel is as close to perfect as it can get. I even shot my laser transit through the bore just for fun and by gosh, it was as close to perfect as any human can get.

                          Last edited by sschefer; 01-20-2018, 05:22 AM.

                          Comment

                          • Klem
                            Chieftain
                            • Aug 2013
                            • 3507

                            #43
                            sschefer,

                            Nice gun and scope.

                            What was the VLTOR upper like before you lapped it? Was it much out?

                            Comment

                            • bj139
                              Chieftain
                              • Mar 2017
                              • 1968

                              #44
                              Originally posted by Keef View Post
                              Home alone this weekend so I didn't get the stink eye for pulling the tool bag out. Lol.
                              Just took it apart for the third time and it took a wooden down and mallet to make it happen. Here are the pics it's a super thin layer but it makes a big difference.
                              [ATTACH=CONFIG]10858[/ATTACH]

                              [ATTACH=CONFIG]10859[/ATTACH]
                              According some bolt action rifle bedders it has less thermal expansion/contractions than some much more expensive products. But I don't really know.

                              Upper face after truing. You can see much more material was removed from one side.
                              [ATTACH=CONFIG]10860[/ATTACH]
                              The BCA side charging upper I lapped did not show that much difference from side to side but it was noticeable.

                              "Are you playing with those guns again? When are you going to fix the dishwasher?" LOL.

                              Comment

                              • sschefer
                                Bloodstained
                                • Jan 2018
                                • 26

                                #45
                                Originally posted by Klem View Post
                                sschefer,

                                Nice gun and scope.

                                What was the VLTOR upper like before you lapped it? Was it much out?
                                It was pretty good, Inside it was a little tight because it was coated but the lapping removed that and then I dry lubed it. They claimed it was dry lubed to begin with and it was probably just fine but I chose to remove the coating and polish it and then dry lube. The area where the barrel extension lives was tight and I would have had to freeze the barrel to avoid using a hammer to seat it. The front end was out .008 down and right. Had I not checked it I probably would have just adjusted to it but once I knew about it, it would drive me crazy if I didn't fix it. My overall opinion of the VLTOR MUR upper is that it's an excellent piece and I would not be hesitant to use it again.

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