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Question about chasing concentricity. . .

Discussion in 'Handloading and Reloading' started by edwardware, Mar 18, 2017.

  1. Walkalong

    Walkalong Moderator

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    Definitely sounds like seating is where the "crooked" comes from. Now to eliminate the cause.
     
  2. Bart B.

    Bart B. Member

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    Instead of one or two V blocks contacting the front and rear of the case body, use one for the pressure ring next to the extractor groove to spin in but a washer whose hole is the diameter about mid point on the case shoulder positioned so it's aligned with the rear V block and cases lay straight. Push the case into the washer so it fits snug in the washer hole like a case shoulder fits the chamber shoulder when fired. Put the dial indicator plunger about 1/10" back from the bullet tip
     
  3. Walkalong

    Walkalong Moderator

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    What about ball bearings or v block at the rear, with a thin v block up front for the shoulder to ride in with a stop at the rear to hold the case from moving back and forth when turning keeping the thin block in place on the shoulder? It would be interesting to compare the two ways and the results. Just thinking out loud.

    As a machinist, he should be able to do whatever he wants with it.
     
  4. Walkalong

    Walkalong Moderator

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    Or maybe a thick "washer" with a shoulder cut in it to push the case into with an adjustable stop at the rear. It would have to be lined up perfectly. Thinking out loud again.
     
    Bart B. likes this.
  5. rsrocket1

    rsrocket1 Member

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    Why are you full length sizing for a bolt gun? Have you tried neck sizing only? Of course you should full length size the first time you shoot the brass, but you should be able to shoot several more times just by neck sizing.
     
  6. Bart B.

    Bart B. Member

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    Because it was proved in the late 1950's that barrels shoot bullets from them more precisely than otherwise. Such cases center the bullet and neck better in the bore than neck only sized cases. Cartridges don't lay in the bottom of the chamber when fired.

    The first indication was when really good 30 caliber match bullets came out, new cases shot them more accurately than neck sized fired ones. Suddenly dawned on the thinkers that all those new cases were full length sized in their manufacturing process. They centered bullets in chamber throats and leads without the interference neck only sized cases with out of round case bodies did interfering with chamber walls. I used to shoot matches with the Sierra Bullets ballistician (bless his departed soul) who was one of the pioneers championing full length sizing bottleneck cases head spacing on their shoulder.

    Plus, full length sizing dies keep the case body and shoulder perfectly aligned with the case neck when sized. Neck only sizing lets the case shoulder and body bend where ever they want.

    Benchrest folks started full length sizing near 20 years ago. Their smallest groups stayed the same size. The biggest ones shrunk.

    Several dozen reloads per case if the die neck is sized right and the die's set correctly in the press.
     
    Last edited: Mar 21, 2017 at 5:18 PM
  7. WelshShooter

    WelshShooter Member

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    Question for you Bart. When you talk about full length sizing for bolt-action rifles, are you talking about the correct setup procedure for full length sizing per the die instructions, or are you talking about full length sizing where the shoulders are only bumped back (e.g. 0.002"), or does this not matter?
     
  8. Bart B.

    Bart B. Member

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    Welshshooter,

    A minimal shoulder bump is best; .002" average is good. Die instructions ensure sized cases will fit SAAMI minimum chamber specs; about 98.7654321% of the time.

    If you can control sized case headspace to a .001" spread, then bump shoulders back only .001". You'll need to have the bolt face squared up first else the case heads' out of square issues won't allow consistent grad clearance. Head clearance is the space between bolt face and case head when the firing pin has pushed the case full forward in the chamber before the round fires. Too much head clearance allows more case body stretching when fired. Too little can bind the closed bolt and it won't be in battery exactly the same for every shot.

    Out of square case heads and bolt faces cause horizontal shot stringing when two lug bolts are in battery and the lugs are at 12 and 6 o'clock. 1/4 to 1/2 MOA horizontal stringing is common. It's caused by the bore axis wiggling horizontally as the bullet leaves the barrel caused by horizontal flexing of the receiver.

    PS:
    My 7th great grandfather in my Dad's lineage was born in the southernmost extent of Wales, in the Glamorganshire region. He came to what's now Jamestown, VA, in 1673. The acreage he claimed is now a parking lot in a shopping center.
     
    Last edited: Mar 22, 2017 at 11:50 AM
  9. Bart B.

    Bart B. Member

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    Yes, yes! A thousand times; yes!

    If I may state that decades old saying. The heck with the few ten-thousandths inch the shoulder is out of round. Sometimes it's best to be a "smarter" Aleck than a dumb one. Kudos to you.
     
    Last edited: Mar 22, 2017 at 11:45 AM

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