Building first Grendel- what are common pitfalls.

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • pinzgauer
    Warrior
    • Mar 2011
    • 440

    #16
    The fact that BCA told you they would "make sure it was headspaced" is bothering me. That's not even a question you should really have to ask. They're either in-spec or they're not.

    It should not be an extra step or something they do as a courtesy. It has to be done when the barrel is being set up.

    Comment

    • LRRPF52
      Super Moderator
      • Sep 2014
      • 8569

      #17
      Originally posted by zcostilla View Post
      THIS is EXACTLY the kind of info I was hoping to find. I have 20 years of military service, so not new to the AR platform at all; and this is my second AR build, but I had no idea what I was doing the first time, and a friend who is a gunsmith helped me build it. (I sold it without really getting to get it set up exactly right because I had a bill to pay and chose to sell an asset I stead of going into debt).

      I really wanted a 20” for a RLGS, but couldn’t pass up a Bear Creek Arsenal 18” Cyber Monday sale for under $60. I ordered a stripped bolt for another $19 and they said they’d make sure it was headspaced. I’ll be using MILSPEC bolt parts for reliability. I was unaware of the port sizing issues, so I’ll DEFINITELY take it to heart. I knew people were recommending adjustable gas blocks for mid-Length barrels but never knew exactly why. As soon as the barrel arrives I’ll measure it with a dial caliper to plan accordingly. I haven’t selected a BCG yet, but I’ll keep it standard weight. I do have a standard rifle length buffer tube and standard rifle buffer. I was planning on 10-round AA magazines, because of AA’s reputation for reliability. For what this rifle will be used for, I don’t need more capacity. Anything else I might have missed?
      I spent a lot of my childhood and adolescence studying the AR15 history, all the parts, internal workings, and began shooting them in the 1980s. I spent 10 years active duty in the Army in units that shoot quite a bit, to include high volume range sessions (sometimes even exceeding 1100 rounds in a day though an M4), was panic-buying and building AR15s because of the Clinton AWB of 1994 throughout my time in the Army, and then got into working on AR15s a lot when I got out and went into the private sector. I learned a lot from some armorers and gunsmiths in the Fort Bragg area, things I never even thought of.

      Since then, I've spent a lot of time working with coalition partner militaries in Europe, which has included a lot of high volume training in Arctic conditions. That has been a real eye-opener to see guns run hard in -30˚C in the snow and ice, going back and forth between brutal sub-freezing temps and getting hot. I also started collecting older surplus parts for retro builds with a preference for parts from the early 1960s.

      Combined with getting into 6.5 Grendel in the AR15, a lot of little things have jumped out that I never knew were right under our noses.

      Even after years of study and hands-on experience with M16A1s, M16A2s, M4s, and M4A1s ranging from extreme cold weather to the jungles of Panama and the Middle East, that experience amounts to almost nothing compared to what I've learned since then about the technical details of the design, but laid a very important foundation to understanding how the guns are actually employed and maintained.

      The more I study and learn, the more I realize how much there is to learn and that the learning should never cease.
      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

      • zcostilla
        Warrior
        • Aug 2017
        • 110

        #18
        Originally posted by pinzgauer View Post
        Well, for one thing... Bolts don't set headspace. Barrel extensions do. The bolt is either in spec or it's not. Headspace is set on a jig when the barrel is set up and pinned. So if it's not right, it's the barrel.

        Once headspace is set up, the gas port is drilled. So hopefully it will be in alignment. You won't be able to tell until you assemble it to the upper.


        The fact that BCA told you they would "make sure it was headspaced" is bothering me. That's not even a question you should really have to ask. They're either in-spec or they're not.

        It should not be an extra step or something they do as a courtesy. It has to be done when the barrel is being set up.
        Yes, I understand that’s how headspacing works. It’s fairly common know,edge. And the customer service rep basically guaranteed that it would headspace correctly. Sorry I didn’t word that more clearly. I didn’t mean to imply that it was an extra service.

        That said, I don’t see how the way I worded it would give the impression that I don’t know anything about what I’m doing. I do have 20 years of military experience, including three years in an Air Control Squadron, where we trained to do our own defensive posturing, convoy defense, and other tactics. Every person in our unit had at least one weapon assigned as their primary (I was ALSO an M-60 gunner for foxholes and HMMWV defensive response). Our training in the weapon was not the typical Air Force minimalistic stuff. I know I’m new here, but not a total novice to the AR platform.

        I was looking for Grendel specific information, because I’m new to this cartridge and know enough to know that the minor changes in configuration for the Grendel can make a BIG difference (ie gas pressure from a different caliber, bolt face depth/extractor, etc.) I’ve received a lot of great responses and I’m certainly thankful for all the tips. Please keep them coming. And thanks for letting me vent.
        -Zac

        Husband, Father, Veteran. Grateful for my redemption.

        Comment

        • zcostilla
          Warrior
          • Aug 2017
          • 110

          #19
          Originally posted by grayfox View Post
          As to the stripped bolt and adding to what '52 said, be sure to get a grendel 0.136 style extractor. A complete grendel bolt will of course have it on there but you're saying a stripped bolt... don't use a 7.62x39 or even a 5.56 extractor, their groove etc dimensions differ from what you need in the Grrrr. There are some threads on this and even a couple of pics, I'll see if I can track them down.

          this sticky has good details. Remember, grendel extractor for 0.136 depth boltface.

          Guys, I've created an infographic to try and show the issues involved in using either a 0.136- or 0.125-inch bolt-face depth in 6.5 Grendel ARs. If you assume the extractor is the same overall length and has the same extractor pin location as a standard 5.56 extractor, then a 0.125 bolt-face depth requires a weakened extractor


          shopalexanderarms.com is your first and best source for all of the information you’re looking for. From general topics to more of what you would expect to find here, shopalexanderarms.com has it all. We hope you find what you are searching for!


          Custom AR-15 Rifles, Custom Uppers, Custom Lower, 6.5 Grendel, AR15, AR 15, AR-15, AR15 upper, custom upper, Lilja, DPMS, Precision, Precision Firearms, Precision-firearms, percision firearms, custom upper, custom ar, custom ar15, barrels, rifle barrels, Shilen, CAA, Command Arms, Yankee Hill, Yankee Hill Machine, 204 ruger, .204 ruger, 223 wyld

          (when in stock)


          (note the specific 0.136 face depth)
          Thank you for the reminder. This is something that would be a crucial error.
          -Zac

          Husband, Father, Veteran. Grateful for my redemption.

          Comment

          • zcostilla
            Warrior
            • Aug 2017
            • 110

            #20
            Originally posted by LRRPF52 View Post
            I spent a lot of my childhood and adolescence studying the AR15 history, all the parts, internal workings, and began shooting them in the 1980s. I spent 10 years active duty in the Army in units that shoot quite a bit, to include high volume range sessions (sometimes even exceeding 1100 rounds in a day though an M4), was panic-buying and building AR15s because of the Clinton AWB of 1994 throughout my time in the Army, and then got into working on AR15s a lot when I got out and went into the private sector. I learned a lot from some armorers and gunsmiths in the Fort Bragg area, things I never even thought of.

            Since then, I've spent a lot of time working with coalition partner militaries in Europe, which has included a lot of high volume training in Arctic conditions. That has been a real eye-opener to see guns run hard in -30˚C in the snow and ice, going back and forth between brutal sub-freezing temps and getting hot. I also started collecting older surplus parts for retro builds with a preference for parts from the early 1960s.

            Combined with getting into 6.5 Grendel in the AR15, a lot of little things have jumped out that I never knew were right under our noses.

            Even after years of study and hands-on experience with M16A1s, M16A2s, M4s, and M4A1s ranging from extreme cold weather to the jungles of Panama and the Middle East, that experience amounts to almost nothing compared to what I've learned since then about the technical details of the design, but laid a very important foundation to understanding how the guns are actually employed and maintained.

            The more I study and learn, the more I realize how much there is to learn and that the learning should never cease.
            I just want you to know how encouraging and how insightful nearly every one of your posts that I’ve read have been. Though I am confident in my understanding of the AR platform, I know that my limitations to a MILSPEC configuration and gunsmith help building my first reveal limitations to my knowledge. We all would do well to remember that we can learn from nearly every experience, positive AND negative. I had a friend from the Smokey Mountains who was raised by his Grandma, and she used to always tell him “If you can’t listen, you can feel.” I always encourage my kids to learn from my mistakes, so they won’t have to make them on their own.
            -Zac

            Husband, Father, Veteran. Grateful for my redemption.

            Comment

            • LRRPF52
              Super Moderator
              • Sep 2014
              • 8569

              #21
              Gas tubes and alignment
              Another hiccup point I see with a lot of the new generation of DIY AR15 builders is gas tube quality and alignment. For me, I always just paid close attention to it and figured that it needed to be as centered as I could possibly get it.

              One technique is to set the upper upside down and use your stripped carrier to test-fit articulation between the gas key and the flange on the gas tube that seals up into the carrier, as this duplicates carrier location in the raceway when under cartridge stack spring tension. Check alignment of the gas tube with the carrier by sliding it back and forth in the area where the gas key opening engages the flange on the gas tube. In AR15 diagnosing, we call it "clipping" when the key and tube bind against each other, causing wear.

              This is most difficult on RLGS, and easiest on pistol or CLGS.

              Gas tubes are not created equally, and many out there will wear quickly, especially if they are mis-aligned. As soon as the flange wears down, the gun will short-stroke.

              Bill Alexander used medical grade stainless tubing for his gas tubes. Not sure if AA does it anymore, but it was a feature on the rifles for many years that most never knew about.

              For military armorers, there are procedures to ensure correct gas tube alignment, and it is part of the TDP for inspections on rifles and carbines for the military.

              Carrier Keys
              Carrier keys are not created equally and most on the market are not made to the Mil-Std or Spec. A lot of companies figured they should harden the carrier key, whereas the TDP calls for the key to be softer so that it doesn't wear the gas tube.

              With the growing wave of nitrided parts, AR15 manufacturers just ask their BCG suppliers to nitride everything, figuring it's better that way than the "lowest bidder" Mil-spec, assuming that engineers, designers, and military inspection/certification contract officers haven't been working on these components since the late 1950s.

              LPKs
              Lower parts kit selection is another area that gets overlooked.

              I was helping a good friend of mine with his 300 BLK build the other day. Took out the LPK and looked at the hammer, which was totally different than any other LPK hammer I've seen in decades. I got to looking more closely at it, and saw that the reinforcement rib along the length of the hammer was missing on the right side, which is what the M16A2 hammer needed in order for the Burst disconnector clutch arm to have clearance.

              It looked like someone reverse-engineered the M16A2 hammer, minus the Auto Sear hook on top for some reason. Maybe a foreign MIM shop took samples of Foreign Military Sales M16A2s sold to them, who knows. The MIM'd hammer also had surface cavitation from shrinking after cooling. Maybe it would be a great hammer, and maybe not. Most of us drop in quality after-market triggers anyway, but I've sometimes used standard hammers for JP FCG set-ups, bobbing the hammer if it was a quality one with good metallurgy and inspection and proof codes. That hammer I would not install in a lower after inspecting it.

              If you ever get a chance to compare Colt hammers, triggers, disconnectors, selectors, bolt catches, detents, springs, bolts, carriers, gas rings, etc. next to whatever the mix of the month is of after-market small parts, you might be surprised at just some of the differences you can see with the naked eye.

              Gas Rings and Carrier Bores
              Gas rings and carrier bore machining/chrome lining are another failure point. On a poorly-machined/finished carrier bore, you will have tool marks galore. Chroming over them doesn't help, and they will grind the crap out of your cheap gas rings for breakfast.

              This is why I check my carrier bores for uniform smoothness before installing them in a rifle. Not all gas rings are made from Mil-Std alloys, so the cheap ones will wear quickly, allowing fouling to flow past them.





              Every little part on a true Mil-Spec gun has a history behind it that may or may not have had early issues, which were then fixed with metallurgy, processes, testing, and refinement.

              The after-market doesn't seem to care much about a lot of these areas, and goes for the cheapest imitation parts they can source from wherever they source them from to make good margins.
              Last edited by LRRPF52; 12-02-2017, 07:19 PM.
              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

              • pinzgauer
                Warrior
                • Mar 2011
                • 440

                #22
                And I didn't mean to imply that you did not know how a ARs work, etc.

                At the same time, there's a large history of people who try to piece together a Grendel from a variety of parts that have challenges that are largely avoidable. And sometimes the manufacturers peddling parts don't help that.

                Talking about headspace is one of those danger signs I have found.

                Due to some of the early manufacturers trying to use 762x39 bolts areas that add complexity with some companies selling Grendel stuff.

                Use of the weaker/incorrect bolt is not really a "set the headspace" issue as much as it would in create an extremely dangerous excessive headspace condition.

                So there's long litanies and tales of Woe with people buying off-spec bargain barrels and or bolts and having issues making it work.

                Thus the recommendation from most that if you're just getting started and not familiar, start with a known good barrel and bolt combination. SAAMI chamber, proper Grendel compound throat, etc.

                I'm wishing I bought one of the barrels that you bought, so no worries there. And hopefully this thing will go right together and play well for you. I have not found Grendel to be picky once you learn about bullet seating depth and things of that nature in reloading that are less forgiving than bolt guns.

                Comment

                • pinzgauer
                  Warrior
                  • Mar 2011
                  • 440

                  #23
                  Originally posted by LRRPF52 View Post
                  Carrier Keys
                  Carrier keys are not created equally and most on the market are not made to the Mil-Std or Spec. A lot of companies figured they should harden the carrier key, whereas the TDP calls for the key to be softer so that it doesn't wear the gas tube.

                  With the growing wave of nitrided parts, AR15 manufacturers just ask their BCG suppliers to nitride everything, figuring it's better that way than the "lowest bidder" Mil-spec, assuming that engineers, designers, and military inspection/certification contract officers haven't been working on these components since the late 1950s.
                  What's your read on the nitrided vs hard chrome keys?

                  I was pondering that the nitride might be a little bit easier on the gas tube bell then the hard Chrome as it's a bit softer. I did used a nitrided alconyl/stainless tube on one recent mid-length build that I liked.

                  Like you say... Parts is not parts. Huge differences between LPKs and BCGs.

                  I used to use Daniel Defense trigger groups until the ALG ACTs came out which are my current favourite if I don't go with a premium trigger.

                  DD, LMT, Colt, or toolcraft/AOP contract bolt carriers all have noticable finish differences compared to generic delton/dpms/whatever. To me it's not worth cutting corners there.

                  They are not cheap, but I'm very pleased with the later production AA bolts with the ionbond whatever coating. Much nicer bolt than my early AA non hard use bolt or generics.

                  Comment

                  • LRRPF52
                    Super Moderator
                    • Sep 2014
                    • 8569

                    #24
                    The underlying base alloy and hardness of the steel gas key is what is called out in the TDP, followed by hard chrome lining of the bore inside of it.

                    The internal diameter has to be within a very tight spec, just like the gas tube flange has to be within a very tight spec for OD.

                    Same with the bolt tail and the bolt tail bore in the carrier that it protrudes through. If that is off, the gas system is too open and will leak there.

                    With modern manufacturing methods, we don't normally see a lot of problem areas here, but if you ever have short-stroking, they are some additional points to look at on top of loose keys, mis-aligned blocks, loose blocks not press-fit to the journal, loose tube-to-gas block fit, etc.

                    Gas blocks press-fit to the journal is another one. The TDP calls for the sight tower/gas block assembly to be fit tightly to the barrel without leakage, then pinned with the taper pins of course.

                    I don't recall seeing much gas leakage on any of my issued M16s and M4s, but I see it all the time on low profile gas block AR15 DIY builds and after-market Vismod AR15s.

                    The LaRue Stealth 2.0 gas system is really nice, functions the smoothest I've felt so far of all my Grendels. He uses a little ferrule to secure the gas tube into the gas block so you don't have leakage there.

                    The ArmaLite AR10 SASS and the KAC Mod 2 gas systems are interesting improvements over the basic tube insertion with tiny roll pin to secure.
                    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

                    • Frontier Gear
                      Warrior
                      • Nov 2017
                      • 772

                      #25
                      Originally posted by LRRPF52 View Post
                      I don't recall seeing much gas leakage on any of my issued M16s and M4s, but I see it all the time on low profile gas block AR15 DIY builds and after-market Vismod AR15s.
                      Yep, It's amazing that such a basic piece as a gas block can vary so much. My buddy decided to go into the gas block business and I was shocked at how much thought he put into it. It paid off though. They aren't 100% leak proof, but are better than most that I've seen. Basically it boils down to quality materials, good tolerance control and tapering the roll pin hole. Some of the cheap imports either leak a bunch or can be a real bugger to install.

                      AXIS MFG Gas Block.png
                      Engineer, FFL and Pastor

                      Comment

                      • zcostilla
                        Warrior
                        • Aug 2017
                        • 110

                        #26
                        Based upon the info given in this thread, I looked up more information specific to the 18” BCA barrel I ordered. BCA website it uses 300BLK feed ramps and 0.070” gas ports. Will I need an adjustable gas block? I wonder if anyone here has an 18” BCA barrel with up with a standard gas block.
                        -Zac

                        Husband, Father, Veteran. Grateful for my redemption.

                        Comment

                        • Frontier Gear
                          Warrior
                          • Nov 2017
                          • 772

                          #27
                          Originally posted by zcostilla View Post
                          Based upon the info given in this thread, I looked up more information specific to the 18” BCA barrel I ordered. BCA website it uses 300BLK feed ramps and 0.070” gas ports. Will I need an adjustable gas block? I wonder if anyone here has an 18” BCA barrel with up with a standard gas block.
                          I'm running an 18" BCA barrel and standard gas block. No issues. I wouldn't expect any either as long as you don't put a suppressor on it.
                          Engineer, FFL and Pastor

                          Comment

                          • zcostilla
                            Warrior
                            • Aug 2017
                            • 110

                            #28
                            Originally posted by Frontier Gear View Post
                            I'm running an 18" BCA barrel and standard gas block. No issues. I wouldn't expect any either as long as you don't put a suppressor on it.
                            Thanks for weighing in! It sure simplifies things if I can use a standard gas block. I’m not planning on suppressing the rifle. And thank goodness for YouTube, as I can see how the alignment pins really make this easier to install everything.

                            -Zac

                            Husband, Father, Veteran. Grateful for my redemption.

                            Comment

                            • zcostilla
                              Warrior
                              • Aug 2017
                              • 110

                              #29
                              So I couldn’t pass up another sale, and ordered a complete 6.5 Grendel BCG from Bear Creek Arsenal. My BCA barrel arrives tomorrow (ordered on Cyber Monday) but I had to divert it to a UPS store because I’ll be at my son’s basketball tournament. I also ordered a nitrided gas block and SS gas tube from JoeBob Outfitters, and arrival time is TBD on the BCG, gas block, and tube. Since they’re Christmas gifts from my wife I have to wait until we get back from FL to install them, so it won’t matter. Only things left to get are magazines and a scope. Looking at a used Redfield Widefield 6X on eBay if it sells under my max bid. Not a fan of Kentucky windage, but it was made before Redfield’s quality took a dump, and will work for close in stuff. If I don’t win the auction it might be another month to get the SWFA SS in 6X, unless the demo in 6x9 HD is still a available. As much as I prefer a fixed power scope, the HD glass at a modest price increase might be too much to pass up.

                              So any magazine brands/models to avoid? I’m looking at 10-rounders.
                              Last edited by zcostilla; 12-08-2017, 04:23 AM.
                              -Zac

                              Husband, Father, Veteran. Grateful for my redemption.

                              Comment

                              • Frontier Gear
                                Warrior
                                • Nov 2017
                                • 772

                                #30
                                They have six of these in stock. I'm 95% sure they are E-Landers.



                                I have hit-and-miss luck with the C-Products mags.
                                Engineer, FFL and Pastor

                                Comment

                                Working...
                                X