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Thread: 308 Win and 308 Obermeyr Difference

  1. #1
    Join Date
    Feb 2004
    Location
    Texas
    Posts
    115

    Question 308 Win and 308 Obermeyr Difference

    Hello Folks,
    Could anyone explain the difference in a 308 Win and the 308 Obermeyer chamber?
    T.I.A.
    Floyd

  2. #2
    Join Date
    Nov 2004
    Location
    Youngsville, NC
    Posts
    1,014

    308 Winchester and 308 Obermeyer

    Boots Obermeyer's reamer print is page 185 in the Pacific Tool and Gauge Gunsmiths Book of Chamber prints. The 308 Winchester reamer print is on page 189 of the same book. Not wanting to violate anyones propriatary rights I will not post the prints.

    The Obermeyer reamer appears to be .4737 in the web. .4450 at the body/shoulder juncture. The neck diameter is .3440. The throat diameter is .3085. The lead is 2.1277 and the throat is 2.2824 long.

    The Winchested reamer appears to be .4738 in the web. .4551at the body/shoulder juncture. The neck diameter is .3442. The throat diameter is .310. The lead is 2.1388 and the throat is 2.3515 long.

    Hope this helps.

    Nat Lambeth

  3. #3
    Join Date
    Feb 2004
    Location
    Texas
    Posts
    115

    308 Win and 308 Obermyer

    Thank you Nat. Next ouestion. So the case is slightly smaller in areas. So therefore would a .298 bore 307 groove 13.5 twist bore be more suited to the Obermeyer chamber versus the 308 Win?
    I'm just trying to understand the .298 bore and Obermeyer chamber combination and the benefit of it versus the 308 Win.

  4. #4
    Join Date
    Dec 2007
    Location
    Brisbane, Australia
    Posts
    2,397
    You need to consider these dimensions with respect to the specs for .308 brass & projectiles.

    What the Obermenyer & other such chamberings do is provide for less slop between standard case & chamber in an attempt (usually successful) to enhance target performance, particularly Palma shooting. These chamberings can benefit from better precision dies like the Redding competition series by reducing unnecessary case expansion in critical areas which predisposes neck bushings to iron the neck out more concentrically - essentially, the more you have to squeeze the neck back, the greater the risk that it will do so out of alignment. The minimum clearance throat gives better alignment between projectile & bore.

    All of this is incidental to bore dimensions - unless the groove diameter exceeds .3085".

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