BCG Recommendation needed

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  • Kswhitetails
    Chieftain
    • Oct 2016
    • 1914

    #16
    Bwild, this actually makes perfect sense. I've been reading all about guys building their rifles and changing things from mil-spec to the extra-super-dooper-pooper, magic-coated, lightweight yadda yadda yadda, on the FB ar15 forums. And man I gotta say, aside from getting some wild takes on the form and appearance of the Armalite platform, there's very few good ideas that pop up, and even fewer long term modifications that make the rounds.

    Your post reminds one that changing the platform from as-designed to "my-spec" brings all kinds of potentially new stress points, wear points, and weak points that were previously designed into the robust machine works of the "original" design. Light weight is nice, but serious engineering should be done to ensure that the necessary materials and strength requirements are met by the new forces placed into the system. I wonder how much of the "broken bolt" label the Grendel got was because of guys making changes to the system in a hasty effort to improve on a proven platform? And as research showed, the devil is indeed alive and well in the details.

    Not that I don't understand the draw toward the newest and shiniest, but sometimes the "good old" are really hard to improve.

    I am rather rapidly growing into the guy that wants poly belted radials on his 68 GT Fastback because that's how it was originally intended... Gosh, am I getting old Nuggin?
    Nothing kills the incentive of men faster than a healthy sense of entitlement. Nothing kills entitlement faster than a healthy sense of achievement.

    Comment

    • bj139
      Chieftain
      • Mar 2017
      • 1968

      #17
      Originally posted by Bwild97 View Post
      Sorry SH, I strongly disagree to the use of a lightweight carrier for the 6.5 Grendel. I have experimented extensively with carrier weights and found that the heavier the reciprocating assembly is the better (to an extent).

      The reason more mass is better, goes like this. As the high pressure gas makes its way through the gas tube and then the gas key, the gas is then directed to the gas expansion chamber behind the bolt,

      the expanding gases push the bolt forward (BEFORE) the carrier begins to move rearward. (Here is where the carriers mass comes into play) the amount of force the bolt gets to move forward (ever so slightly)

      is directly related to the weight of the carrier.

      The forward motion of the bolt is important because it allows the locking lugs of the bolt and extension to slightly separate while the bolt rotates to disengage from the extension.

      Most people will never know this to be an issue until they start breaking bolts and getting accelerated cam pin wear. You can monitor the issue by watching the wear pattern on the back side of the bolts locking lugs,

      if they appear to be smearing or rounding off with metal squishing off them, you should add some weight to the reciprocating assembly.
      ^^^^^^ THIS +1
      If you analyze the situation you will see this is how the BCG unlocks.
      This is an ingenious aspect of the AR Stoner design.

      Comment

      • LRRPF52
        Super Moderator
        • Sep 2014
        • 8569

        #18



        It helps to understand how the system works. The Stoner Internal Expansion operating system is very interesting in that it combined 2 traditional parts into one to eliminate excess weight and off-centric reciprocating mass (things moving around that are not in-line with the barrel).

        Once you start playing with mass, things can get away from you really quick.

        For initial builds on 16" MLGS or 20" RLGS, I recommend selecting a quality, true Mil-Spec carrier and a quality Grendel bolt.

        We don't even know what gas system, barrel length, and port diameter the OP has, or what ammunition he plans to shoot.
        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

        • Peregrine
          Bloodstained
          • Dec 2017
          • 30

          #19
          Thank you Bwild97. Your explanation makes a lot of sense. I really want to understand the system before I decide which components and specs are most advantageous to utilize in my build. This is exactly why it takes me awhile to decide on the right parts to purchase.

          As much as I'd love a highly tuned rifle, that would be impossible to achieve without a solid understanding of the original system design and function. I want my first build to utilize quality components which work together to form a reliable system. I'm most interested in learning how to achieve the best possible balance of forces that control the cycling action. Early on I read a lot about DI vs Gas Piston and I came to the conclusion that a simpler system is a more reliable system (less is more). Based on my understanding of how the system cycles, it seems like an adjustible gas block would help to achieve this. That being said, there seems to be quite a few variables that ultimately control how the system cycles:

          Mass of the BCG
          Length of the gas system
          Gas port diameter
          Buffer weight
          "Strength" (probably the wrong term) of the buffer spring

          I've read a bit about variations in the dimensions of Grendel bolts and extraction problems. That's why I want to opt for a higher quality bolt. I know the BCSs get pretty dirty, so something like a melonite coating would help me to keep the inner workings clean. I'm a fan of both BCM and LMT. I know I will most likely pay a bit more, but sometimes that's worth piece of mind. No it doesn't have to be the best, but I want to ensure all parts function reliably. I've been looking into Toolcraft as well. I may pick up a JP SCS system, because I've heard the pogo stick sound after every round when firing my friends ARs and it drives me nuts (I've got a little bit of OCD.) What I really enjoy is a firearm that you can tell is high quality and well thought out when you pick it up and fire it. It doesn't need to be fancy to do that, just well designed.
          Last edited by Peregrine; 12-28-2017, 04:33 PM.
          Gun control means using both hands.

          Comment

          • Peregrine
            Bloodstained
            • Dec 2017
            • 30

            #20
            LRRPF52,

            These types of conversations are EXACTLY why I joined this forum. I eat this stuff up. I have an elementary understanding of how the gas system works. Now I want to dig into the details.

            Originally I wanted to purchase the best quality barrel I could for the money. I was on the PF website a lot and almost bought a fluted Criterion barrel. What killed the deal was the intermediate length gas system, it seemed somewhat rare and I read somewhere (probably here) that the intermediate gas length system would cause unreliable cycling. I opted for the 18" group buy barrel because it seemed to have all the right specs, mid-length gas system, 0.750 diameter gas port, and most importantly it is SAAMI spec. It should serve me well for my first Grendel build.
            Last edited by Peregrine; 12-28-2017, 04:32 PM.
            Gun control means using both hands.

            Comment

            • StoneHendge
              Chieftain
              • May 2016
              • 2009

              #21
              I’ll take up the JP argument later since I’m on the road today (I’ve got to defend my crack dealer) but Peregrine, JoeBob Outfitters has complete Toolcraft 6.5 grendel BCGs for 99 bucks. I don’t think anyone here can’t argue that isn’t a screaming deal. And if he has anything else you need and you spend $150, you get a free T-shirt and maybe one day when your walking down the street, someone will walk up to you and say “JoeBob dun saved you money!”
              Let's go Brandon!

              Comment

              • Peregrine
                Bloodstained
                • Dec 2017
                • 30

                #22
                Thanks for the heads up SH. 😃
                Gun control means using both hands.

                Comment

                • NugginFutz
                  Chieftain
                  • Aug 2013
                  • 2622

                  #23
                  Originally posted by Kswhitetails View Post
                  Bwild, this actually makes perfect sense. I've been reading all about guys building their rifles and changing things from mil-spec to the extra-super-dooper-pooper, magic-coated, lightweight yadda yadda yadda, on the FB ar15 forums. And man I gotta say, aside from getting some wild takes on the form and appearance of the Armalite platform, there's very few good ideas that pop up, and even fewer long term modifications that make the rounds.

                  Your post reminds one that changing the platform from as-designed to "my-spec" brings all kinds of potentially new stress points, wear points, and weak points that were previously designed into the robust machine works of the "original" design. Light weight is nice, but serious engineering should be done to ensure that the necessary materials and strength requirements are met by the new forces placed into the system. I wonder how much of the "broken bolt" label the Grendel got was because of guys making changes to the system in a hasty effort to improve on a proven platform? And as research showed, the devil is indeed alive and well in the details.
                  I'm getting titanium scope caps, a carbon fiber dust cover and a skeletonized hand grip for mine. Then I'm going to get a BCG with a full race cam...
                  Originally posted by Kswhitetails View Post

                  Not that I don't understand the draw toward the newest and shiniest, but sometimes the "good old" are really hard to improve.

                  I am rather rapidly growing into the guy that wants poly belted radials on his 68 GT Fastback because that's how it was originally intended... Gosh, am I getting old Nuggin?
                  fill in the blank) in our everyday guns. Sure, it makes sense to cut weight where it matters. In my opinion, though, much of these gadgets, gimcracks and gewgaws are nothing but solutions in search of a problem.

                  Feel free to take issue - I, too, once owned a '63 Chevy Belair which had every conceivable bolt on accessory the local auto-parts supplier could provide. All my efforts managed to reduce the value of that beauty by 1/2.
                  If it's true that we are here to help others, then what exactly are the others here for?

                  Comment

                  • Kswhitetails
                    Chieftain
                    • Oct 2016
                    • 1914

                    #24
                    Fuzzy dice? On an AR? Man, you ARE getting old... I feel much better, ahem, younger.
                    Nothing kills the incentive of men faster than a healthy sense of entitlement. Nothing kills entitlement faster than a healthy sense of achievement.

                    Comment

                    • StoneHendge
                      Chieftain
                      • May 2016
                      • 2009

                      #25
                      Let's go Brandon!

                      Comment

                      • Frontier Gear
                        Warrior
                        • Nov 2017
                        • 772

                        #26
                        Originally posted by StoneHendge View Post
                        Frontier compared a JP carrier to an exotic sports car. Having had the privilege of being handed the keys to a shiny yellow 360 Modena about a dozen years ago and being allowed to take it for a spirited drive, I guess its a valid comparison - except a JP operating system will cost you a few hundred bucks more instead of a few hundred thousand more.
                        It's all in the percentages The JP carrier is about 6.5 times the cost of a standard BCA carrier. So my $40,000 Chevy is now an exotic and super fun $260,000 sports car. Heck, if that's what is fun for you and you can afford it then by all means go for it.

                        I just thought that the OP had $675 left for all the rest of his parts (including the barrel) based on another thread. http://www.65grendel.com/forum/showt...l=1#post177286

                        So spending $400 didn't seem like a good fit for the budget. However, I understand that those glamour shots of new hardware with the shiny metal can sometimes change the budget figures a bit
                        Engineer, FFL and Pastor

                        Comment

                        • bj139
                          Chieftain
                          • Mar 2017
                          • 1968

                          #27
                          Since Peregrine brought up gas syetem length:
                          I have a ballistic Advantage 18" barrel with a rifle length gas system and it is the only barrel I own where I have problems with ejection.
                          I think this is because an 18" barrel should have a mid length gas system for longer dwell time.
                          I have to shoot this more and see if it breaks in or I have to drill the gas port larger to compensate.

                          I bought a BCG with DLC (diamond like coating) from Delta Team Tactical. It was only $10 more than the NiB bolt.
                          I will post my opinion after I receive it tomorrow
                          Last edited by bj139; 12-28-2017, 10:54 PM.

                          Comment

                          • Bwild97
                            Warrior
                            • Jan 2015
                            • 217

                            #28
                            The "ILGS" (Intermediate Length Gas System) is perfect for the 18" and 20" tubes! I have built a few Rifles using Odin Works barrel kits. Using a rifle buffer assembly and standard Mil. Spec. BCG, provided perfect operation from the very first round and continue to operate flawlessly! One of these rifles has had nothing but a steady diet of WPA ammo (Wolf Steel Cased) and no cycling issues to date.

                            Bj,

                            My 18" Rifle is RLGS as well, and had some issues with cycling reliably; so began my BCG weight and buffer spring experiments. Only after a few tear downs did I realize that the gas block journal was cut for the spacer plate that is used in the standard clam shell type HandGuard, moved the Gas block forward 1/16th" and voila! Perfect operation!! It's worth a look.




                            Race parts for Race Rifles, I don't think many serious 3Gun and timed event competitors are going to be using a 6.5 Grendel in competitions. I understand the need for "shiny and cool", but it will always come at an expense. The "LMOS" systems are designed around 5.56/.223Rem chambered rifles, not the more powerful alternatives.
                            Last edited by Bwild97; 12-28-2017, 11:51 PM.

                            Comment

                            • grayfox
                              Chieftain
                              • Jan 2017
                              • 4295

                              #29
                              One caveat on the toolcraft bcg gentlemen in case it hasn't been mentioned before: the bolt and the firing pin need to be used together since the TC bolt is 0.011 shorter than a standard AR bolt, and the firing pin as well. Just re-checking myself on both of these that I currently have in my formerly 6.8-spc-stained fingers (hahahaha!!!) before writing this... my TC pin is 3.266-3.267", my standard pin is 3.279".
                              So don't borrow the TC pin to use in the monster-group buy bolt, or other standard bolt; use it only along with the TC bolt. Caliper the bolt and pin you're going to use together, if in any doubt.
                              "Down the floor, out the door, Go Brandon Go!!!!!"

                              Comment

                              • bj139
                                Chieftain
                                • Mar 2017
                                • 1968

                                #30
                                Bwild,
                                Thanks for the gas block information. I will check out the gas block alignment, maybe stick a toothpick in there.

                                Comment

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