Coned bolt

Discussion in 'Gun Project Questions & Gunsmithing' started by clowdis, Dec 7, 2013.

  1. clowdis

    clowdis

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    When you're cutting the barrel fora coned face bolt, do you try to match the boltface angle or do you add some clearance like 5 degreees or so? For instance, if the boltface cone is 120 degrees, do you cut the relief in the barrel to 30 degrees or, say, 25 degrees to add some clearance?
     
  2. Eddie Harren

    Eddie Harren Gold $$ Contributor

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    I cut the same angle but allow .005" for BR rifles and .010" for rifles that will fire more than 7-10 rounds per match.
     
  3. Erik Cortina

    Erik Cortina Team Lapua Brux Borden Captain Gold $$ Contributor

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    Cut cone to same degree but allow clearance like DocEd said. If you change the angle, you will have more clearance inside the cone than outside or vise versa.
     
  4. clowdis

    clowdis

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    For instance, Barnard recommends a 20 degree angle in the barrel to match the 60 degree (120 degrees total) bolt face angle. I don't see the extra clearance hurting anything, but was just curious.
     
  5. butchlambert

    butchlambert Site $$ Sponsor

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    It isn't any trouble until you have an accident.
     
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  6. X Ring Accuracy

    X Ring Accuracy Site $$ Sponsor

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    Cut same angle, just give the clearance
     
  7. gunsandgunsmithing

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

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    Proper clearance and angle between the bolt nose and barrel does two things...makes sure that there is NOT too much unsupported case, and meters gas in the event of a case separation.
    Set it where you are most comfortable knowing that.
     
  8. butchlambert

    butchlambert Site $$ Sponsor

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    Thank you Mike.
     
  9. gunsandgunsmithing

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

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    I was thinking of you when I posted it. ;) I was trying to do an impersonation of you. ;D
     
  10. clowdis

    clowdis

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    Mike,
    Changing the angle of the barrel cone doesn't change the amount of clearance at the bolt face. In fact, the decreased angle might actually give a little more support to the case head, although I doubt that's its enough to make any kind of difference. The ones that really bother me are the 1903 Springfields and the pre 64 Winchesters, not Barnards or Pandas, etc.
     
  11. gunsandgunsmithing

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

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    You're right, and I've seen smiths cut the breech end of the barrel flat. What's gained and what's lost, though? The coned breech aids feeding, and if mated properly with the bolt nose angle, will help meter escaping gas if a case were to separate, for whatever reason. That's not to say that it will prevent gasses from escaping altogether, or that if there is enough pressure, from, say an overcharge, that it won't be destroyed, rendering it useless, but nevertheless, is a safety mechanism that is best left in place,IMO.


    Have you ever read up on the Remington "three rings of steel" concept? It's based around gas containment.
    That's why it utilizes a counterbore in the barrel for the bolt nose to fit inside of. The clearances around, fore, aft and radially are critical to it working as designed. They are designed so the bolt nose will expand into the counterbore, largely containing gasses and debris in the event of a overcharge induced case failure. It's a proven system...better in this regard than coned bolts. Savage and Sako use flat breeches but have a baffle in the bolt raceway to help protect the shooter, for the same reason.


    To answer, yes, what you propose can be done, but at reduced safety. The push feed Winchesters don't have either and work well. The positive to this is that you can have less unsupported case than with a counterbore, such as Remington has.
     
  12. clowdis

    clowdis

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    Can't argue with any of what you said. The Remington system is pretty solid from a safety standpoint, better than the cone breech systems I think. The coned breeches do feed better though, can't argue with that either. The ones that I like are the bolts with a 120 degree cone angle, that way I can leave the lathe compound set at 29 degrees where I was threading and cut the cone angle with a 1 degree relief.
     
  13. Erik Cortina

    Erik Cortina Team Lapua Brux Borden Captain Gold $$ Contributor

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    Yes, like the Panda's. The sell cone reamers, but for an oddball, you might as well bite the bullet and move the compound.
     
  14. jscandale

    jscandale

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    I did an HS Precision the other day which has a 35° cone and a flat at the base of the cone. As a side note; after having worked with this action, I'll say that I am very disappointed in the it. From the price that HS charges for their rifles, I was expecting something much more than a modified Remington clone that wasn't quite as nice as the original.

    JS
     
  15. TRA

    TRA Silver $$ Contributor

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    I think the "Three Rings of Steel" was more a result than a design. It's simple to manufacture and cheap. The result was a win win for the PR folks. When there's a catastrophic failure the gas cannot be contained, it must be released. I've seem hundreds of photos of a Rem style bolt with the nose of the bolt burned off. Not something I would care to experience. Why is it that these cutting torch disasters very seldom involve a cone faced bolt? Maybe the perceived advantage is nothing more than hype.
     
    Last edited: Jan 13, 2018
  16. Robert

    Robert Silver $$ Contributor

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    It is most certainly because they need to allow clearance for the extractor?. Not a good design feature!!

    General recommendation is same angle with.008.
    R.G.C
     
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  17. GenePoole

    GenePoole

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    I had a customer request a tight clearance (0.005 - 0.007) on a switch barrel for his Defiance Rebel action. I recommend against it but he showed me a document from Defiance that said these tolerances are acceptable for BR type builds and I complied, but he brought it back complaining of marks on the barrel cone. I told him it was probably from dry cycling. He had 0.010 of bolt slop. I showed him the math and he agreed and had me shave a few more thou off it to the recommended spec (0.012 - 0.015 IIRC).

    I use a piece of electronics solder and a small dab of grease to hold it in place to measure the clearance. I have a handy little mic with a round mandrel to measure the curved piece of solder that comes out.

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  18. Will Henry

    Will Henry

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    The cone can be cut flatter than on the bolt and there is no problem but if the cone is more acute, the amount of exposed case is greater. No reason not to cut it the same if you are going to cut it at all. I always go for .005" clearance and accomplish this by cutting the cone deliberately shallow. I then insert the bolt into the receiver and screw the action on to the barrel until the bolt contacts. I then use feeler gauges to determine how far I have to go. So. if the barrel shoulder is .031 away from the receiver face, I cut the cone .036 deeper and there you have it. I use a dial indicating on the carriage to set the cut.
    I am quite sure Remington (Mike Walker) did deliberately engineer the "three rings of steel" into the 722 action. Had they not, there would have been no reason for the counterbore at all and the lugs could have gone right to the end of the bolt. The Remington does do a good job of sealing the high pressure gas in the event of a case failure. A coned breech does not and does no better than a flat breech in this regard. WH
     
  19. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Silver $$ Contributor

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    Will,
    Exactly the method I use. I duplicate the angle and achieve my clearance with feeler gauges.

    A lot of people don't realize the 3 rings of steel provides a labrynth seal for gases as well as the namesake protection from catastrophic failure.

    --Jerry
     
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  20. gunsandgunsmithing

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

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    I can't agree with this. Sure, if enough pressure is applied, anything can and likely will fail.
    One reason the bolt nose comes completely off in some cases is if the counterbore is too big, id. Again, .003-.005" is the designed clearance. The bolt nose can only be expected to yield so far before it breaks off.
     
    Last edited: Jan 14, 2018
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