Why 6 BRA?

Discussion in '6BR, 6BR Improved & Wildcats' started by Curious, Oct 28, 2017.

  1. BoydAllen

    BoydAllen

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    All other things being equal, rate of fire has a lot to do with throat damage. Cases conduct the heat to this large head sink that they are chambered in, and they are ejected after firing. Barrels, especially those used for long range benchrest are routinely subjected to rapid strings of fire that build throat temperature. On the neck length thing. Do some asking around about the 6mm Remington vs. the .243 Winchester on barrel life.
     
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  2. Sheldon N

    Sheldon N Silver $$ Contributor

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    I suppose another way of thinking of it rather than as some sort of angular flame point convergence, is to ask the question "Where the powder is located in the brass/barrel when it ignites?". In a straight walled pistol size case the powder closest to the primer ignites first and starts to launch both the powder ahead of the already burning powder plus the bullet down the barrel. The more the case is a bottleneck shape, the more it restricts the powder from being launched down the bore before it is fully burned. Case like the 243 Win would allow a good chunk of burning powder to be launched into the throat, where as a 40 degree shoulder case with a shorter/fatter powder column and a longer neck is going to help keep that powder burning inside the case.
     
  3. Jet

    Jet Gold $$ Contributor

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    Fire formed 95 pieces of brass with 29.9 gr of Varget, BR400 primers and Berger 108s seated to just touching. Did a barrel break in process on a new Krieger at the same time for the first 40 or so rounds. Shot at 100yds and the wind was switching back and forth a good bit so I didn't really attempt to shoot anything small. The group below is when the wind settled down and I watched the flags. .3" for 12 shots. As a side note. Velocities stayed steady for shots 3-45 then climbed a few fps every few rounds up to shot 80 then it settled down for the last 15 shots. Ended up 50 fps faster when I finished. Looking forward to getting some load testing done.

    IMG_1124.JPG
     
  4. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    Pretty interesting to watch the barrel speed up like that huh? One of our local shooters mapped a couple new Kriegers with every shot over the lab radar for the first 150. It was cool to see the velocity curve as the barrel sped up. Theres only one barrel I know of that does not speed up and you can do load development on day 1, but they wont tell me what grit they use to lap them or I be re-lapping our Kriegers ;) I have to believe its in the surface finish.
     
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  5. 1911mag

    1911mag Silver $$ Contributor

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    Question has anyone built one on a Bartlien 5R barrel and have had sucess? Not opposed to other brands just favor that barrel from past sucess.
     
  6. Jesse Gietzen

    Jesse Gietzen

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    our engineers are experimenting with different lapping grits right now, as well, although likely for different reasons. i have two guesses as to which barrel manufacturer you're referring to, but am curious. i think you may be right about surface finish.
     
  7. Steelnecktie

    Steelnecktie

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    I’d guess Rock Creek.
    I’d like to know if surface finish has something to do with cold bore shot. Seems like the Proof Research carbon barrels hold a pretty good cold bore shot compared to other barrels.
     
  8. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    I have lapped barrels with 80-180 AO and SC grits. If you bore scope new barrels during the break in process you will see a very obvious change in the surface finish. Especially on the tops of the lands. I am not sure the original lapped finish plays a huge role after the barrel has broken in. I have never had a coppering problem, but I have not gone finer yet. I think volume plays a bigger role in coppering. Some barrels never see a lap and seem to be ok. I dont think Douglas laps.
     
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  9. JohnMill

    JohnMill Gold $$ Contributor

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    I always appreciated Ackley's pioneering ( I think ) And the same for Alex Wheeler. Hope to buy something from you someday
     
  10. JohnMill

    JohnMill Gold $$ Contributor

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    I believe that if someone were to dredge up the Precision Shooting article on Turbo Point chamber design, it might answer any or all/some of those questions
     
  11. tom

    tom Gold $$ Contributor

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    I found this tonight looking for something else. Below is pictures of the chamber end of a dasher and BRA. Both are exactly 100 rounds fired. I have to be honest, I kind of stopped using the borescope. It seemed like my stuff all of a sudden "didn't last as long" lol.


    Dasher 100 rounds182738.jpg




    BRA 100 rounds_182156.jpg


    Not that it matters, I would change barrels every day if it made me shoot smaller:D


    Tom
     
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  12. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    I didnt know you were into antique camera equipment.
     
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  13. tom

    tom Gold $$ Contributor

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    It's a cellphone picture of the display screen. Don't have any fancy stuff, spent all my money on gunsmith bills!

    Tom
     
  14. urbanrifleman

    urbanrifleman Gold $$ Contributor

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    What are we seeing?
     
  15. johnnyi

    johnnyi Gold $$ Contributor

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    I'm assume the first photo are from the dasher with very early sighs of wear (if you can see those lateral lines) at the start of the throat just in front of the case mouth. vs the second photo looks like a freshly cut chamber which I assume is the BRA. Yet he is saying they have the same number of rounds down the bore. Early indications favoring the BRA in barrel wear...?
     
  16. urbanrifleman

    urbanrifleman Gold $$ Contributor

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    On the left, is that firecracking?
     
  17. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    The vertical line is the chamfer at the end of the neck at the beginning of the free bore. The neck is to the right and the freebore is to the left of this line. That saw edge look on the top picture is erosion starting in the throat. Thats a very big difference to see that early on.
     
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  18. daniel brothers

    daniel brothers Silver $$ Contributor

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    I can't tell if it's a boy or a girl... need better glasses I guess.
     
  19. Toby Bradshaw

    Toby Bradshaw Gold $$ Contributor

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  20. comagutsa

    comagutsa

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    i used lab radar on my 6BRA barrel from 1st shot.. started at 2751fps , 120 rounds later I'm at 2820fps
     
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