300grn 338, seating depth?

Discussion in 'Reloading' started by 7mmrowland, Jul 6, 2009.

  1. 7mmrowland

    7mmrowland Well-Known Member

    Oct 2, 2008
    What are you guys finding for seating depth on the sierras 300grn 338 bullets that shoot the best are they in or out of the lands and all that good stuff?
  2. specweldtom

    specweldtom Well-Known Member

    Jun 7, 2004
    I've only shot them in a .338 x .378 Wby, but the longest load I've tried is 4.00" OAL. That still leaves me with .115" of freebore in my factory dimension chamber. I don't intend to get any closer to the rifling than that. I have seen 1/2 moa groups in several custom Wby Boomers with factory magazine length ammo, so the 1/4"+ freebore that they're shooting through doesn't seem to hurt accuracy. The 300gr Smkhp's are too long to seat to mag length in my opinion and need to be single loaded. If you decide to shoot the 300 gr bullets in loads that exceed magazine length and in chambers that have a lot of freebore, you'll have a lot of room to experiment with oal. I wouldn't get closer than .100" off the rifling, but you should still be able to find a sweet spot.

    Stay safe, Tom

  3. mmmooretx

    mmmooretx Well-Known Member

    Jul 7, 2009
    Barnes says 0.050 back from contact with lands.
  4. royinidaho

    royinidaho Writers Guild

    Jan 20, 2004
    I rig up a dummy case that "just" holds the 300 SMK. I then let the chamber seat the bullet.

    That usually results in the best of everything, velocity and accuracy.

    The action is a 700 REM single shot and loaded that way. A loaded round can be barely extracted. Cartridge is 338 RUM chamber is factory.
  5. Joel Russo

    Joel Russo Official LRH Sponsor

    Jul 5, 2006

    All of my .338-.408's like the 300 SMK between .005" and .015" off the lands.
    I've had them on, and just "in" with no appreciable gain in accuracy.