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How much can crimping affect pressure, etc?

Discussion in '10mm Reloading Forum' started by OregonG20, Sep 19, 2012.

  1. OregonG20


    Sep 5, 2011
    I have a fairly light crimp on all my loads, .422. I am happy with their performance, but just curious as to how much crimping can affect a load. I have seen some loads crimped to .419. I would assume this adds to the pressure, but does it add to the velocity? I am not a velocity hound, and my loads are very accurate in my gun, just posing the question for discussion.

    Speculation can be fun, but I was wondering if anybody has actually gone through different crimp amounts and chrono'd the data.
  2. nickE10mm

    nickE10mm F.S.F.O.S.

    Apr 13, 2004
    Wichita, KS
    I would guess that the final crimped diameter might not even necessarily correspond to the AMOUNT or TIGHTNESS of the crimp itself... but that's just a guess.

    Still, I've heard of more than a few people that will use crimping to get a little more velocity out of slower powders (Longshot, for example) to "let the pressure build a bit more behind the bulle" but that would also be at the expense of more pressure.

    Just rambling... :p sorry
    Last edited: Sep 19, 2012

  3. Any Cal.

    Any Cal.

    Oct 27, 2008
    I think the crimp makes almost no difference. If you pull a round out of a crimped but unsized case, there is very little resistance. The neck tension is what actually does something.
  4. OhioGlockMan


    Mar 1, 2010
    Akron, Ohio
    For what its worth, I used to buy into the heavy crimp theology untill I started playing around with the Rainier plated bullets last summer which actually require you to use only enough crimp to get rid of bell so round will chamber. I started running them over the chronograph and thought hmmm the same charge weights im used to with jacketed yielded the same velocity, accuracy was great. So I started giving the jacketed and cast loads light crimps and same thing, velocity was the same, accuracy great so I now no longer heavily crimp anything
  5. Taterhead

    Taterhead Counting Beans

    Dec 13, 2008
    Boise, Idaho
    A heavy crimp will actually cause less neck tension. Crimping to the point of reducing the diameter of the bullet just undersizes the bullet and causes less brass grip at the point the crimp. I pulled a couple hundred rounds gunshow ammo for components. They were new brass and should have had plenty of neck tension since the heal of the bullets bulged the brass a little. Some were crimped significantly ~ 0.418". Those plopped right out with the kinetic puller. All had noticable indentations on the bullets. The ones crimped properly took more work to pull.

    It was consistent. The bullets crimped heavily had little neck tension. Those that did not held tightly.
    Last edited: Sep 20, 2012