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Another New Upper

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  • Another New Upper

    Milldawg inspired me so I finished my new 6mm AR upper as a Covid time killer project. I had made a 6mm Creedmoor with an 8 twist Bartlein barrel for a friend of mine and he returned it for a new barrel after about 3000 rounds. It had been a real shooter capable of 0.1" groups but had bad throat erosion and a heavy ceramic-like carbon in the first third of the bore. Regular solvents had no affect on the carbon so I cleaned it with Semichrome and 22" of the riflling looked pretty good. The muzzle was severely worn for the last 1/8" of the crown so I cut off 1/2" and re-crowned it. I cut off about 3 1/2" at the chamber end.

    I decided to make a 21 3/4" AR15 barrel out of it, chambered in the 6mm AR wildcat (a 6.5 Grendel necked down to 6mm). I bought about $400 worth of AR upper parts and turned down the barrel to AR specs with an 0.800" gas block. I used a Redding Type-S 6.5 Grendal full length sizing die with a 6mm bushing to do the neck-down and a 6PPC seating die. It willl shoot up to 109g match bullets. It will hopefully be accurate to 1000 yards with the right bullet.

    Here are a few pics: Click image for larger version

Name:	Origninal Bartlein Barrel.jpg
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ID:	741954Click image for larger version

Name:	Cutting Off Bad Throat.jpg
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ID:	741955 ​​​​​​​
    Attached Files

  • #2
    Smooth lookin' AR D'Man!
    Let us know how it shoots. 😃!

    Comment


    • #3
      Originally posted by DakotaMan View Post
      Milldawg inspired me so I finished my new 6mm AR upper as a Covid time killer project. I had made a 6mm Creedmoor with an 8 twist Bartlein barrel for a friend of mine and he returned it for a new barrel after about 3000 rounds. It had been a real shooter capable of 0.1" groups but had bad throat erosion and a heavy ceramic-like carbon in the first third of the bore. Regular solvents had no affect on the carbon so I cleaned it with Semichrome and 22" of the riflling looked pretty good. The muzzle was severely worn for the last 1/8" of the crown so I cut off 1/2" and re-crowned it. I cut off about 3 1/2" at the chamber end.

      I decided to make a 21 3/4" AR15 barrel out of it, chambered in the 6mm AR wildcat (a 6.5 Grendel necked down to 6mm). I bought about $400 worth of AR upper parts and turned down the barrel to AR specs with an 0.800" gas block. I used a Redding Type-S 6.5 Grendal full length sizing die with a 6mm bushing to do the neck-down and a 6PPC seating die. It willl shoot up to 109g match bullets. It will hopefully be accurate to 1000 yards with the right bullet.

      Here are a few pics: Click image for larger version

Name:	Origninal Bartlein Barrel.jpg
Views:	211
Size:	22.8 KB
ID:	741954Click image for larger version

Name:	Cutting Off Bad Throat.jpg
Views:	82
Size:	68.3 KB
ID:	741955
      What kind of powder was your friend using and didn't he ever clean it ?

      Comment


      • #4
        That's a nice project! Have you tried the 6.5 Grendel and if so, what's your opinion of it?
        Trump 2020 - Keep America Great!

        Comment


        • #5
          Originally posted by jhjimbo View Post

          What kind of powder was your friend using and didn't he ever clean it ?
          He used H4350 and the Berger 105g Hybrid. He cleaned it religiously but didn't know about carbon ring until I saw the barrel. Overbore cartridges cause immense heat at the throat that melts a ceramic-like carbon to the steel of the bore. It is heavier at the first few inches of the bore but can extend down the barrel over time. Regular solvents can't remove it so when he used his regular cleaning solvents, they did nothing to the carbon ring in the bore. Semichrome metal polish (invented in Germany for cleaning carbon build up from semi truck chrome exhaust stacks) melts it better than anything known. It took me about 8 iterations of swabbing the bore to remove all the carbon and the bore was pretty good underneath. Most people think their barrel is burned out when they see the cracked carbon that looks like pitted steel in a bore scope. As you might imagine, accuracy deteriorates as this carbon ring builds up and it is hard as steel, deforming bullets as they pass over it.

          The sharp rifling edges on crowns erode from the carbon bearing high pressure gas over time too, radically degrading accuracy; especially with big, heavy-for-caliber boat tail bullets. It makes them yaw out of control. I re-crown my competition rifles every 400 rounds to keep crowns sharp and predictable for long range shooting. This one had over 3000 rounds on the original crown and it was seriously torn up. The same crown damage occurs over time when you clean your rifle by shoving the cleaning rod into the muzzle end of the bore as well. We must treat our crown like like a new born baby.
          Last edited by DakotaMan; 08-13-2020, 02:14 PM.

          Comment


          • #6
            Originally posted by PigHunter View Post
            That's a nice project! Have you tried the 6.5 Grendel and if so, what's your opinion of it?
            I haven't tried the 6.5 Grendel PH. It is a pretty powerful close range cartridge for its size but it isn't fast enough with those heavier bullets to get me the long range precision I desire. I wouldn't hesitate to use it on hogs. It would be marginal for penetrating the shield of a charging 350+ pound boar but it would be fine if you hunt out of a tree stand where you have a better chance of picking your shot.

            Comment


            • #7
              I have heard certain powder kernel shapes are more abrasive than others on the rifling. Maybe that kind should be used to keep the carbon from forming.
              I have often thought of a duplex charge of part powder and part inert particles that would help keep the deposits from forming on the rifling.

              Comment


              • #8
                Originally posted by jhjimbo View Post
                I have heard certain powder kernel shapes are more abrasive than others on the rifling...
                There may be something to that jimbo. However, I'm constrained to the few powders that shoot with supreme accuracy for a given cartridge, bullet, bore and barrel length. As I understand it, all over-bore cartridges are going to melt carbon to the steel when exposed to the high temperatures encountered during the short while the heavy bullets are overcoming their inertia within the bore. I clean it out of my 25-06, 25 Creedmoor, 22-6mm, etc. the same way. I also accept that barrels will eventually wear out if you really enjoy shooting them a lot just like gas disappears in your tank when you go somewhere. There is no doubt in my mind that cleaning the carbon ring out extends their life though... maybe double.

                Comment


                • #9
                  Originally posted by FirstBubba View Post
                  Smooth lookin' AR D'Man!
                  Let us know how it shoots. 😃!
                  Thanks Bubba.

                  Comment


                  • #10
                    Nice rifle.

                    Comment


                    • #11
                      Thanks Milldawg... you inspired me... how is your's shooting? I'm going to have to wait a while... I received a .223 bolt carrier group instead of the 6.5 Grendel BCG I ordered for this one. I borrowed a friend's bolt to complete the headspacing but returned it before I noticed the error.

                      Comment


                      • #12
                        Haven’t got the lower done yet working and trying to get our retail store build out done.

                        Comment

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