6BRA Donut Management

Discussion in '6BR, 6BR Improved & Wildcats' started by Curious, Jan 5, 2018.

  1. Curious

    Curious

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    My first batch of cases has suffered quite badly with donuts, I cut into the neck/shoulder junction as much as I would normally do but it hasn't stopped them appearing after the first couple of firings.

    Ive cut them out but plan to start again with some new brass and would be keen to see some examples of what amount of neck/shoulder material is enough to avoid them.

    Below is a piece of new brass that I cut a little deeper into the neck/shoulder, I would welcome thoughts from those who have managed to remain donut free on whether this is enough or too much?

    Im using a 40 degree blade in my K&M cutter and a loaded round is .265

    IMG_2488.jpg

    IMG_2489.jpg
     
    Last edited: Jan 5, 2018
  2. Curious

    Curious

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    Donuts cause flyers in my experience regardless of neck length or where the bullet is seated Stan.

    In the past Ive seen them cause havoc with groups and once removed accuracy and consistency returned to normal.

    This is the first Ackley case I have ran so its something new for me. My normal level of neck turning has worked fine with cases like standard BRs, Dasher, 6.5x47 Lapua and many others so I was surprised to see such a problem with my 6BRA so soon.
     
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  3. Rushty

    Rushty Gold $$ Contributor

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    I am completely donut free, 200 pieces of Lapua, 2 firings on a 100 and 3 firings on the other 100.. mines a .272 no turn chamber and I don’t turn the brass.

    Cheers Rushty
     
  4. Northridge

    Northridge

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    My experience with 6BRA is donut is really none existent but good luck let us know how you do.

    Shawn Williams
     
  5. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    I have never seen a doughnut cause issues when the bullet was not seating into them. Lots of records set with doughnuts. Careful cutting into the neck too deep, that can cause a problem.
     
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  6. Curious

    Curious

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    Are donuts a common problem then with the 6BRA then in your experience?
     
  7. Alex Wheeler

    Alex Wheeler Gold $$ Contributor

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    They are not a problem at all. Bullets dont seat that deep. I have never seen the gas choke point theory hurt a thing. In the BRA when you form the case it pulls some of the neck down into the shoulder so doughnuts are even less likely.
     
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  8. CaptainMal

    CaptainMal Silver $$ Contributor

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    Just saw this and run a pin probe into the few cases I have that have been just twice fired. Smooth inside.
     
  9. dkhunt14

    dkhunt14

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    It should be like Alex says. When they are formed part of the neck forms into the shoulder. When I turn Dashers I stop about a sixteenth inch short of junction. Once they are fireformed, the turned part is now halfway down the shoulder. That's makes it so there is no donut. The 6BRA should be the same but you would have to turn to the junction. Be careful how hard you turn into the shoulder. If you shoot a neck down your barrel, it will ruin your day. Matt
     
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  10. dkhunt14

    dkhunt14

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    How many times were they fired? How do you know you have a donut? Matt
     
  11. johara1

    johara1

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    if you can't live with the donut, use a a K&M carbide mandrel and cut them out. What you are feeling is the neck shoulder junction that doesn't expand like the rest of the neck. ...jim
     
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  12. dmoran

    dmoran Gold $$ Contributor

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    If seating bullet shank at the shoulder/neck junction, issues can arise, donuts or not.
    With improved cartridges that are blown forward, donuts are highly unlikely if neck turned to the original junction. But have seen some that ended up getting a taper (donut effect) after a few firings when they stopped neck turning to far in front of the junction.
    Donovan
     
    Last edited: Jan 6, 2018
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  13. mikecr

    mikecr

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    Donuts affect a load when they're brought into neck tension.
    How do you define a donut? That is, how is it presenting?
    Do you FL size necks?
    Do you seat bullet bearing into donut area?
     
  14. johara1

    johara1

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    As I said before you never seat the heel of the boat tail below the sized area of the neck. Then none of the issues with the donut or what ever affect anything..... Jim
     
  15. mikecr

    mikecr

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    If donut area is down sized(ID under cal), like with FL neck sizing, then it is brought into tension even where bullet bearing is clear of the fit. This, because any under cal portion contributes to grip provided by brass in actual contact with bearing.
    Expansion helps reduce donut influence here, but it's best to never FL size necks to begin with.

    OP's neck turning should have mitigated donuts. I'd like to understand how this is not the case.
     
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  16. Curious

    Curious

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    I would have expected that also.

    I think I have found the underlying reason although I haven't proven this yet.

    My sizing die wasn't sizing the .200 area enough, I wasn't getting clickers but my brass was always difficult to re-chamber with a tight bolt close. I felt that the F/L sizing die was doing the base enough so when I was checking headspace by dropping the bolt the resistance I could feel was the web not the shoulder, as a consequence I kept bumping the shoulder until the bolt dropped freely then another couple of thou. What I now realise is the resistance to stop the bolt from dropping was coming from the base of the case not its length and I was bumping the shoulder about 8 thou more than it was needed due to the false reading I was getting.

    I have since used a .308 body die to size the base for now and it works great, once sized it allows me to bump the shoulder correctly and the rifle is shooting really well today. I will now turn the new brass in my usual manner and junk these cases as they have had more stress on them than I would like.

    Thanks to Boyd Allen for the PM correspondence :)
     
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  17. foxguy

    foxguy Silver $$ Contributor

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    Thanks for keeping us up dated, What dies were you using for the sizing?

    Thanks,
     
  18. Curious

    Curious

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    I made my own FL sizing die.

    The spec I gave for the resize reamer isn't sizing it enough at the .200 mark so will have it reground.
     
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  19. gunsandgunsmithing

    gunsandgunsmithing The best tuners and wind flags on the market Gold $$ Contributor

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    FWIW, .003" smaller has worked well for me. It yields a case that is about .0015 smaller at the shoulder and about .0005-.0006" smaller at the base, than a case that has been fired a few times with a stiff charge. This is with a variety of cases but all of them that I've had re-size reamers made for have been short range stuff, like PPC and BR cases.
     
  20. steve123

    steve123

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    Tell me if I'm wrong but isn't the diameter of the shoulder decreased significantly using a 308 body die???

    I just got a 20-221AI and it only came with a neck die. I called the smith that did the work and he said to use a FL 223 die to decrease the web area. I tried it and across the shoulder was .006 smaller so...
     

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