308 neck advise

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by pvanwyk, May 31, 2006.

  1. pvanwyk

    pvanwyk Active Member

    Dec 23, 2004
    Busy fitting a new barrel to my 308 and would appreciate any advise regarding the neck size that should be cut, and the reasons why.

    Will be shooting 168gr SMK's, Lapua brass, can neck turn if required.
  2. Coyoter

    Coyoter Well-Known Member

    Nov 10, 2001
    "Busy fitting a new barrel to my 308"

    Then you already have the new barrel?
    There are only a few reasons to neck turn. If you get a tight necked chamber, then you turn to get .004 (I think) clearance on the chamber for minimal working of the case neck. Shoot, bump the neck back down with a neck die, seat a bullet and shoot again.
    If your chamber isn't small enough that you have to turn to make the brass fit, then you're where I am.
    I turn for the obvious reason of consistant neck tension, and to give uniform tension when using a bushing style neck die. Forgive me if this is elementary, but a bushing die pushes the imperfections of your case neck to the inside, if you don't turn then your tensions will be way further off than if you'd simply used an expander ball style of die. Turned and using a bushing die is more even than not turning and using an expander ball, but probably the same as if you turned and use and expander ball.
    Why turn then? For one, less work on the brass. You're taking it from chamber diameter to .003 smaller than the bullet diameter you're shooting rather than to .010 and then expanding it back out to .005 smaller with the ball.
    Two is that Redding Competition dies utalize the bushings and are outstanding dies. With their setup, I get no discernable neck runout and only about .002" bullet runout.
    How much to trim off?
    What I was told and therefore have always done, is to leave the brass as thick as possible with no low spots on 90% of the brass you turn. For my .243 I seem to recall that left me with .014 wall thickness, but don't hold me to that. From there I figured the wall thickness, bullet diameter, neck tension of .003" and ordered 3 bushings, the one I thought I'd need and the ones to either side of it, for my Redding die. It seems to have worked out:)
    Hope all that helps.

  3. Bart B

    Bart B Well-Known Member

    Dec 25, 2005
    I'd get a chamber neck diameter of about .345-inch. That way you can use virtually any cartridge case; thick or thin neck walled. Such chamber neck diameters have been used with cases having .012-inch thick neck walls to shoot many, many sub half-MOA 10+ shot groups through 800 yards. Which pretty much dispels the theory that tight necks have to be used if best accuracy is an objective.

    One nice thing about having lots of clearance around the loaded round's case neck is if it's not pretty straight, it still won't bear against the chamber neck wall which can cause accuracy problems.

    A normal SAAMI chamber reamer at the minimum specs should do fine. Be sure to have chamber headspace set to between 1.630- and 1.631-inch.
  4. Desert Fox

    Desert Fox Well-Known Member

    Jan 31, 2002
    Mine has .343 neck. It's an Obermeyer design reamer for 175 grain bullet. Shoot's Sierra or Nosler 168 very well. 155 Scenar is even better. Use strickly Federal gold medal match brass, neck turned just for uniformity. My barrel is Pac-Nor Supermatch 12 twist 3 grove.