6.5 Grendel Group Buy Bolt 1/ Barrel Extension 0

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  • sneaky one
    Chieftain
    • Mar 2011
    • 3077

    #16
    You are both lucky, and unlucky. You could have been injured big time. Good to hear you are okay, sorry to hear of gun damage. Call a lawyer yet? Don't hand over any parts just yet.

    The extension needs to be checked for proper metallurgy, and not from the company that manufactured it!

    I have never seen this type of ext. failure before, Geeeze....
    Last edited by sneaky one; 01-08-2018, 11:29 PM.

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    • Texas
      Chieftain
      • Jun 2016
      • 1230

      #17
      Originally posted by dtdraffen View Post
      Ouch!
      Wow never seen that happen..
      Sorry for what happen to you
      If I am understanding this correctly, you had a catastrophic failure of a bolt a few weeks ago, switched to a new bolt of the same type (.136), fired the weapon a number of times and had a catastrophic failure of the barrel extension.

      The headspace is maintained between the bolt face and the center of the shoulder of the cartridge. When we were building M16s with absolute milspec components, we would find a barrel that would not headspace, and we would try two or three other milspec bolts, and it might headspace. The chamber , barrel extensions, and bolt all have a tolerance. They are not +000/-000. A combination of these tolerances could collectively cause a headspace problem. Did you check the headspace with a go/nogo guage after the bolt failure? The event could have caused micro-fractures in the barrel extension which finally failed with additional shooting. This would be maginified with excessive headspace.

      It is really fortunate that you or no one else was hurt.

      I will be very interested to hear what Lilja has to say about the barrel and barrel extension.

      Comment

      • brut28481
        Warrior
        • Mar 2016
        • 117

        #18
        I had the upper receiver mounted horizontally and in a receiver vise. I use the wheeler receiver lapping tool with a power drill. I was definitely lucky that I did not get injured. When I originally got the barrel I had some accuracy issues and checked the headspace with the factory Bolt. After that bolt broke and I replaced it with the Grendel Group by bolt I did not recheck the headspace. I did use the blue marking compound to verify proper engagement and did not see anything out of the ordinary. Barrel arrived back at Lilja today. Hoping to hear something soon.
        Last edited by brut28481; 01-11-2018, 12:48 AM.

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        • The Profit Joseph Sith
          Warrior
          • Nov 2016
          • 596

          #19
          Man. Really glad your ok!
          Texas asked a few questions i was wondering like RE checking headspace after first.
          One other question i had is how many times have you used your upper lapping tool before truing this upper? And how tight did the bore fit in the BCG tunnel?

          This is out of my troubleshooting arena one thing im curious about for future reference is, can bolt to extension seating uniformity be inspected by Prussian Blue or soot transfer ir other similar method?

          Id REALLY like to find a way to cast AR chambers WITH the bolt installed to get a FULL dimension slug to inspect. (Especially if i can barrow the optical comparitor at work) there HAS to be a way!
          Maybe plug the barrel 1-2" past throat fill chamber to 90% install bolt with pin hole plugged and extractor dammed and re melt to 302 or less depending on alloy.

          I dont know how confident i am in wheelers tools.. They may be decent but i am a skeptic. I recently got the midwayUSA and was pleased to find out it was made by pacific tool and gage (guage?) Im still rather skeptical of these tool by in large. Dial indicators and true machinist tools are infinitely better.
          One last thought i almost forgot white oak had a decent email about inspection points.
          Last edited by The Profit Joseph Sith; 01-11-2018, 04:35 AM.

          Comment

          • Sticks
            Chieftain
            • Dec 2016
            • 1922

            #20
            Originally posted by The Profit Joseph Sith View Post
            ...
            Id REALLY like to find a way to cast AR chambers WITH the bolt installed to get a FULL dimension slug to inspect. (Especially if i can barrow the optical comparitor at work) there HAS to be a way!
            Maybe plug the barrel 1-2" past throat fill chamber to 90% install bolt with pin hole plugged and extractor dammed and re melt to 302 or less depending on alloy.

            ...
            I think you will get the casting locked in the lug area.
            Sticks

            Catchy sig line here.

            Comment

            • Kswhitetails
              Chieftain
              • Oct 2016
              • 1914

              #21
              Silicone RTV?
              Nothing kills the incentive of men faster than a healthy sense of entitlement. Nothing kills entitlement faster than a healthy sense of achievement.

              Comment

              • Sticks
                Chieftain
                • Dec 2016
                • 1922

                #22
                Getting a good release agent on the bolt, chamber and extension might get a good mold, but then you would be doing very light manual measurements which will increase your +/- accuracy.

                I would do Paraffin wax before RTV
                Sticks

                Catchy sig line here.

                Comment

                • Sticks
                  Chieftain
                  • Dec 2016
                  • 1922

                  #23
                  Cut a case at the 1/3 mark or so, drill out the flash hole to the same bore as the firing pin, get a screw that will fit and affix the cut case to the ejector free bolt, then do your 90% casting and re-heat to flow back into the cut case.

                  What are we measuring again?
                  Sticks

                  Catchy sig line here.

                  Comment

                  • just_john
                    Chieftain
                    • Sep 2012
                    • 1565

                    #24
                    When you lap the outer edge of the upper extension, the upper should be secured vertically ( LR..52 had an excellent discussion relating to this ). When doing this horizontally, the weight of the shaft of the tool causes some droop which then takes the griding face of the tool away from a plane perpendicular to the line of travel of the bolt. Looking at the pictures of the lugs on the bolt, there are marks on the near lugs from contact with the extension but none ( visible ) on the far lugs. This puts all the lock-up strain on a reduces number of lugs - and something has to give.
                    I have been using the Wheeler tool on many builds. It is a simple, rotating tool and works quite well in this application. Any rotating tool will work equally well in this kind of application - you could even use suction cups as long as they are turrning at a reasonably fast rate and get the same results. The key is to keep the center of rotation and angle of rotation in-line with the travel of the bolt and perpendicular to that travel.

                    Comment

                    • The Profit Joseph Sith
                      Warrior
                      • Nov 2016
                      • 596

                      #25
                      Im using hitechalloy's http://hitechalloys.com/hitechalloys_002.htm cerro safe they say to only use a light oil "non detergent" and that will fine for release. The cerro safe which ive used in the past shrink .0005" after cast and in hour is the exact same size. Only prob with that is grows after the hour.
                      Im going to give cerro cast another try this weekend. It shrink .0001" and stays the same size throughout its life.

                      So far i take a little PFTE tape and roll it around a dowel to the I.D. of the lugs in the extension and seat it all the way against the stub to create a wall to keep it out from under the lugs they might scrape a hair when removing but they come out just fine. Its great for throat, lands, neck and shoulder measurements. But id still like to take a full headspaced cast from the bolt back.

                      I just realized... Silly putty!
                      Last edited by The Profit Joseph Sith; 01-11-2018, 02:41 PM.

                      Comment

                      • brut28481
                        Warrior
                        • Mar 2016
                        • 117

                        #26
                        Originally posted by just_john View Post
                        When you lap the outer edge of the upper extension, the upper should be secured vertically ( LR..52 had an excellent discussion relating to this ). When doing this horizontally, the weight of the shaft of the tool causes some droop which then takes the griding face of the tool away from a plane perpendicular to the line of travel of the bolt. Looking at the pictures of the lugs on the bolt, there are marks on the near lugs from contact with the extension but none ( visible ) on the far lugs. This puts all the lock-up strain on a reduces number of lugs - and something has to give.
                        I have been using the Wheeler tool on many builds. It is a simple, rotating tool and works quite well in this application. Any rotating tool will work equally well in this kind of application - you could even use suction cups as long as they are turrning at a reasonably fast rate and get the same results. The key is to keep the center of rotation and angle of rotation in-line with the travel of the bolt and perpendicular to that travel.
                        Hind sight is so clear.....of course that makes total sense to mount vertically!!! Use gravity (KISS Method, keep-it-simple-stupid) I do recall when lapping the finish for the receiver face working off on certain areas more then others first. I thought to myself "I sure am glad I lapped this receiver" Now.....maybe not so much. Operator error? My only reservation about assigning causality to receiver face being out of true from poor lapping is the manor in which the first bolt lug sheared. Following the "drooping" theory, wouldn't you expect more pressure at the top of barrel extension/bolt with those bolt lugs shearing first? If I recall my lug lower to the extractor went...Same goes for when extension went off??

                        Comment

                        • Tex Nomex
                          Warrior
                          • Dec 2017
                          • 185

                          #27
                          Originally posted by brut28481 View Post
                          Aren't 6.5 Grr & Creed interchangeable? It was hard to load but I just kept mashing the forward assist with a hammer......
                          Uhhhhhh..... wut?

                          There being 2 events, it may be hard to determine the true cause.

                          Could have been the original bolt was somehow out of spec, leading to uneven wear on the bolt, on the extension's lug surfaces,... Amazing how fast replacing worn parts can trigger a system failure.
                          "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

                          • The Profit Joseph Sith
                            Warrior
                            • Nov 2016
                            • 596

                            #28
                            I check my uppers with a .0015" feeler gauge and the lapping tool to see if it was square before lapping i didn't want to mess with them if they were good. I tested 7 uppers in one sitting. Both AP slick sixe uppers were slightly out. Two of the four generic Brownells M4 uppers were spot on two were slightly out. (Side note) ALL six ejection port door rod holes were unfinished.. Couldn't believe it.. What are the odds? Luckily i have extended .1250" pilot bits.
                            Hopefully my M4E1 uppers i just got yesterday are better. Although im slightly skeptical of the method it SHOULD result in trueness. Its relatively the same process as used in thousands of rebuilt engines. I DEFINITELY which i had a bed with bearings and a dial indicator to check the lapping tools squareness or run out before i used it.
                            I really dont think its critical at all that the interface between the two is "perfect" although it wont hurt. There is some slop inherently or they would be to tight to function correctly. And a well made barrel has ALOT more to fo with accuracy results than a slight cant.
                            Eager to find out any word on this.
                            Just my $.02..

                            Comment

                            • brut28481
                              Warrior
                              • Mar 2016
                              • 117

                              #29
                              Spoke to Lilja yesterday, they still haven't had a chance to look at it.....

                              Comment

                              • brut28481
                                Warrior
                                • Mar 2016
                                • 117

                                #30
                                Like all great love stories the Ballad of the Lilja barrel extension explosion must come to an end. Lilja has decided to replace the barrel without commenting on the causality of the barrel extension destruction. At this juncture it is probably difficult to determine what the true root cause was. Operator error? Poor Gunsmithing? Hot loads? Like all great Mysteries, we shall never know. I'd like to comment on Lilja's response, they quickly reviewed the situation and without question replaced the barrel. They stand by their products and I think they're a great company! The only one true question remains, should I lap my new Mega upper?

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