Help with Dasher over pressure

Discussion in '6BR, 6BR Improved & Wildcats' started by Waderthemudder, Aug 12, 2017.

  1. Waderthemudder

    Waderthemudder Silver $$ Contributor

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    HI there-
    Im having trouble with two Dashers. Both are gong over pressure with moderate loads.
    Today I did a test on one and I was still getting ejectors marks at 30 grains of H4895!

    The kicker is that I have a third Dasher made with the same reamer that is not showing any signs
    of pressure.

    Both the over pressure guns are vintage 40x repeaters.
    The good one is a Kelbly Atlas repeater.
    All three barrels are krieger 8 twist with the same reamer. I don't know the freebore.

    HEEEEEEEEELP!
    Wade
     
    Last edited: Aug 12, 2017
  2. Mulligan

    Mulligan Silver $$ Contributor

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    Does the Atlas have an ejector?

    The reason I ask, a buddy had been shooting 30.9 gr of Varget in a 6BR panda action. He switch actions to a pande f-class rig with mechanical ejector. Using same barrel he us getting ejector marks...... the original panda didn't have an ejector to leave a mark. All were a bit stout....
    CW
     
  3. skiutah02

    skiutah02 Gold $$ Contributor

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    I had this problem and it was solved by using a 308 Small Base Body die to size the lower portion of the case. Had shot new 6br brass to fire form to 6brx in a different chamber and fireformed brass would often not chamber in second barrel and when it did, very hard bolt lift with moderate loads. Both chambers cut with same reamer by same person. Sized base and all is well.
     
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  4. Waderthemudder

    Waderthemudder Silver $$ Contributor

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    I am using brass that was former in another gun with the same reamer. I full length sized it after forming and it chambers without any resistance. Do you still think that could be the cause???

    There is an ejector in the Atlas Mulligan.
     
  5. kountryboy2

    kountryboy2 Gold $$ Contributor

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    What bullet are you using?
     
  6. skiutah02

    skiutah02 Gold $$ Contributor

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    Yes. I shot a 28-shot string.with all cases FL sized (6Br die since 6BRX) and all 28 chambered flawlessly. But all 28 I had to use both hands with thumbs on the scope rail for leverage to eject (no hammer). Used body die then FL die on same cases. Came back 2 weeks later for another practice match. Was able to eject them with one finger on bolt handle. Measure case head on neck side of groove (right at groove) and youll see.
     
  7. ShootDots

    ShootDots Gold $$ Contributor

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    Here are a few things that can drive up pressure quickly. I have had 2 / .236 bores in Dashers and 2 / .237 bores. The .236 bores could not take anywhere near the powder charges that the .237s could. However, they could take more than you're pushing. If you have a "carbon ring" located in the chamber at the end of the neck where the rifling starts, is a major contributor to pressure. Additionally, if your freebore is short, depending on the bullet, can and will contribute to rising pressure. Finally, if you have an excessive length of the case necks AND IF they are jamming up against the end of the neck of the chamber, you will get pressure. There is at least a reasonable chance that one or more of these "problems" are in existence in your rifle. If not, I am at a loss..
     
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  8. Waderthemudder

    Waderthemudder Silver $$ Contributor

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    Thank you guys I will try all of them!

    Much appreciated!!!
     
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  9. skiutah02

    skiutah02 Gold $$ Contributor

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    All these are great suggestions.
     
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  10. charlieyankeesierra

    charlieyankeesierra

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    I had this problem recently, and I got around it by changing powders. Varget and H4895 gave ejector marks, but RL-15 didn't.
     
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  11. ShootDots

    ShootDots Gold $$ Contributor

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    There had to be something else going on there.. Varget, depending on which lot, can be a 1/2 shade faster or slower than RL-15. Generally, they are nearly identical in burn rate. Even between various lots of Varget, the difference between Varget and RL-15 is almost non-existent. That is why I say that something else has to be afoot there..
     
  12. Hal

    Hal

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    Check for a carbon ring.

    Let us know what you find.

    Hal
     
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  13. charlieyankeesierra

    charlieyankeesierra

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    I'm not the first person to see a difference between RL-15 and Varget in a particular chamber. Anyway, I had the same issue as the OP, and got around it by changing powders.
     
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  14. dkhunt14

    dkhunt14

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    I can shoot more velocity and less pressure with RL15 over Varget. I would imagine
    H4895 is the same because it is faster then Varget. Matt
     
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  15. geraldgee

    geraldgee Silver $$ Contributor

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    I read the your comments several times but don't think you mentioned if these are newly chambered barrels or whether these loads had been shooting fine and then went south. Despite using the same reamer, could the chambers of the 2 problem barrels have excessive headspace? You said you FL sized your brass after fire forming - are you sure that each barrel requires the same shoulder bump on the case? If your dies are set up for one chamber, and you shoulder-bump based on measurements from another chamber, could that potentially lead to a shoulder that is set back .006 - .007 too much?

    i said that to say this - measure your chambers to determine if they are close enough to one another to use the same FL die setting for all three.

    Good luck.
     
    Last edited: Aug 13, 2017
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  16. Pappy42

    Pappy42 Silver $$ Contributor

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    Have you determined that you have enough loaded case neck clearance for your chambers?
     
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  17. Waderthemudder

    Waderthemudder Silver $$ Contributor

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    Ok so the brass is to long on one of the rifles, but the other one seems to be a different problem. It's brass is correct length.

    On the second one the pressure seems to rise slowly over around 30 shots. At 30ish the pressure spikes and brass is near impossible to eject and ruined. If I go back and clean and try again it repeats all over the same way.

    Someone did tell me the think this is bore size being out of tolerance. It's a 237 bore.

    Thanks a bunch for you help on this everybody.
     
  18. dkhunt14

    dkhunt14

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    Setting the shoulder back .006 to .007 will not make more Pressure. If anything it will help relieve pressure by the brass having more room to expand. Also by setting the shoulder back too much in a Dasher you will eventually blank primers. Matt
     
  19. dkhunt14

    dkhunt14

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    Sounds to me like the barrel is fouling too much. Maybe a bad lot of powder. Also maybe could be a carbon buildup in neck area or throat. Are the freebores the same? Matt
     
  20. geraldgee

    geraldgee Silver $$ Contributor

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    Noted with follow question: I prefaced my comment quoted above by asking about excessive headspace. If the headspace was long and the shoulder set back as mentioned, would the firing pin bump the cartridge forward to shoulder contact and ignition then drive it back to the boltface and lead to ejector marks?

    Thank you
     

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