How to over come overbore?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by daveosok, Mar 4, 2005.

  1. daveosok

    daveosok Guest

    I had a long discussion with Dan Lilja a few years ago that lead to the building of a 34 in barreled 7mm stw. Dan had said that the stw case was extreme overbore and that to utilize the case capacity for maximum velocity 34 inches were needed.
    I built the stw and am able to launch 180 Berger behind 74.5 grains of H1000 at 3100 fps.
    I see a lot of posts on here about 6.5mm on huge cases.
    From my conversation with Dan it seems there are two ways to overcome overbore;1) use faster burning power, 2) use extremely long barrels. The latter seems to reach its end quicker than the long barrel length.
    There seems to be some sort of length to case capacity ratio that would net maximum velocity.
    Where is the line drawn or is there even a line for case capacity and bore size.
    This is just a discussion and answers are welcomed in any form.
  2. Mikecr

    Mikecr Well-Known Member

    Aug 10, 2003
    In my view "overbore" can be used to describe a cartridge offering under 1000rnds of barrel life.
    It's original definition was short sighted at best, given that todays powder availability nixes the possibility of actually being overbore(unless you use the wrong powder).
    There are 'magic' ratios described in patents, which affect efficiency alittle. And you can figure that maximum velocity/lowest muzzle pressure for a given cartridge can be had with a particular powder/barrel length combo. But for the most part, -powder amount to bore area- sets barrel life more than anything else.
    This is really the limiting factor w/regards to popularity.
  3. Guest

    Guest Guest

    My limited experence has led me to beleve that slower burn rate powder will work.Example 7mm rem. mag clasic load of 79.5 gr of H870 produces 3100 fps in a 26"barrel,Ruger#1 Accuracy is 1 moa. Another of my experements with a 300 win mag using a surplus powder that was only available hehe in Utah. Ireco 85 Ball powder very slow burn, 84gr behind a 180gr Sierra game king,Fed215 primer,velocity 3200fps 5/8" group 5 shot @100 yds. This is out of a Browning Stainless with the Boss system.This load was pressure tested at Barnes an was at 59100 psi, sammi max is listed at64000psi. With a 300yd zero the drop is -8"@ 400yds. Energy figures to be over 4000 ft lbs more than my .338 win.I found that a premimum bullet would be a better choice fo elk. /ubbthreads/images/graemlins/cool.gif
  4. 1doug

    1doug Well-Known Member

    Feb 15, 2005
    just get Kirby to build you one of those new allen mags and dont worry about over bore. Heck you would never have to worry about under bore or under gunned for any thing (North America) again. just my 2 cents