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Thread: Model 11 first rebarrel, headspace and primer issues

  1. #1
    BFL68
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    Model 11 first rebarrel, headspace and primer issues


    Hi all, first post here. I've built AR-15s and reloaded for about 4 years now, and a buddy and I have decided to branch out into bolt guns. Being left handed, I got my first Savage about 15 years ago and haven't looked back.

    Since we already have ARs chambered in 6.8 SPC, it was natural to go that direction with our bolt gun project. Our barrels are chambered in 6.8 SPC II. The Spec II chamber has a different chamber design in the throat and freebore, all other case dimensions are the same. We built the first one this weekend, and something doesn't seem right.

    Donor rifle was a new M11 Trophy Hunter in .243. We installed the new 6.8 barrel, new recoil lug, and barrel nut. PTG 6.8 bolt head was used. Headspace was set with PTG 6.8 SPC go and no-go gauges. Bolt would just close on the go gauge, not on the no-go.

    We took the rifle out to test fire and sight in. We used Hornady and SSA factory ammo. Brass showed significant case stretching (~.004"), case bulging, flattened and cratered primers. We tried the other factory ammo, same result. We fired one of our starting charge reloads with similiar "overpressure" indications.

    Brought the rifle home and tore it down. Set the headspace with a sized piece of brass, using the "scotch tape" method to set the headspace. At this point, we tried the go gauge. The bolt will not come close to closing on the go gauge. After much discussion and thought, we decided to shoot the rifle, as it chambered factory ammo fine. The sized brass we used to set headspace is the same dimension as we use for our AR-15 reloads, and have no issues with it. Reassembled and back to the range.

    After firing the factory ammo again, brass looks normal. Normal looking brass, no more stretch issues, however the primers are still cratering. Flattened primers have gone away, we did not see them again until we approached the max charge on our load development. Barrel shoots very accurately.

    Long story short, I'm not real comfortable with the bolt not closing on the go gauge. I know it chambers factory ammo from both the manufacturers we normally shoot, but this doesn't feel right. There was approximately 3/4 of a turn difference in the barrel between the headspace from the go gauge and the headspace using the sized brass. Granted, everything feels right, based on the way the brass looks. Should we be concerned about this?

    As far as the cratered primers, they crater no matter factory or reload, starting charge or max charge. They start to flatten as we get to the max charge, which is normal. Since we changed the bolt head, could firing pin protrusion be the cause here? I can't think of any other reason, other than an oversized firing pin hole, that would cause cratering. I'm applying AR logic here, as that is a not uncommon problem with an AR, but this is a bolt gun. Same idea, different mechanics.

    Any insight would be greatly appreciated. At this point, the rifle shoots great, brass looks great, but we are still cratering primers.

    Thank you in advance.

  2. #2
    Basic Member
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    3/4 of a turn in the barrel index amounts to .0375" difference in headspace...something is wrong. I suspect the bolt head is contacting the barrel.

    1. Remove the barrel, and measure the protrusion of the headspace gauge sticking out of the chamber.
    2. Measure the depth of your bolt face.
    3. There should be a minimum of .005 clearance
    "As long as there's lead in the air....there's still hope.."

  3. #3
    MrMajestic
    Guest
    Fred, If he was contacting the barrel how would he be able to make it tighter by 3/4 revolution? What about the ejector hanging him up? Do the go and no-go gages enter the boltface under the extractor with the bolt removed? Just brainstorming here....

  4. #4
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    Quote Originally Posted by MrMajestic View Post
    Fred, If he was contacting the barrel how would he be able to make it tighter by 3/4 revolution? What about the ejector hanging him up? Do the go and no-go gages enter the boltface under the extractor with the bolt removed? Just brainstorming here....
    I would second this suggestion and recommend removing the extractor. Some gauges do not sit square against the boltface if the extractor is attached, they end up canted against the extractor. If that happens it could increase the headspace by a large amount. You would think everything is fine since it closes on the go-gauge but not on the no-go, but in reality the headspace is too long by the depth of the extractor which is probably a few hundreds of an inch.

  5. #5
    BFL68
    Guest
    Thank you for the responses. The barrel is not hitting the boltface with the go gauge, as MrMajestic said, we were able to continue screwing the barrel in when sizing on a new piece of sized brass. The barrel did screw in farther with nothing in the chamber than it did with the sized brass. The gauges do fit inside the bolt face.

    It is possible that the go gauge is hanging up on the extractor. We tried hooking the go gauge under the extractor prior to attempting to chamber it, it still will not close on the go gauge. We will try taking the extractor out and see if that resolves the issue.

    As far as the cratered primers, I'm still at a loss. The firing pin protrusion is .043", and the firing pin hole in the bolt face is .069", which appears to be in spec. The .473 factory bolt head is .070", and it is my understanding that firing pin protrusion is supposed to be .040" +/- .005. The cratering is the same, be it factory loads, starting loads for reloads, or where we stopped on load workup due to other pressure signs (slightly sticky bolt and flattening of primers).

    Thanks again for the help, it is greatly appreciated.

  6. #6
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    Your firing pin fit is close enough, the problem lies on the tip configuration. The tip needs to be "blunted" somewhat, so there is a 90 degree junction at .025" protrusion.
    If the tip has a full radius, the tangent of the radius is below the bolt face at .025" protrusion, leaving a gap for primer cup material to flow into.
    "As long as there's lead in the air....there's still hope.."

  7. #7
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    I don't know anything about tangents, are they good to eat?

    Two pin tips. On the left one as it came new and on the right one I reshaped to the radius Fred is taking about.


    The same two pins set to .020" protrusion in the same bolthead, factory on the left, one reshaped on the right. ( BTW, the butchered bolt head was from a used rifle I bought!)


    Add to that any chamfer on the edge of the pin hole in conjunction with the pin tip allows ton of room for the primer cup to flow into. Many times one will switch primers, a Federal to CCI for example to cure or minimize cratering, but its a Band-Aid, not a fix.

    Bill
    Each morning eat a live green toad, it will be the worst thing you'll have face all day.

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