From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: 308 vs. 30-06.
Organization: Hewlett-Packard Fort Collins Site

Brent Danielson (jessie@iastate.edu) wrote:

: Why is it that handloaded 30-60 can't be made as accurate as a .308
: given the same quality of rifle?

Because the '06 powder charge is longer and heavier.  That tends to
be more difficult to uniformly ignite and delivers a harder blow to
the bullet before it gets into the rifling.

: In fact, I would think that a 30-06 could be more accurate since
: there is the option of loading it with more powder and getting the
: bullet to the mark quicker - thus reducing the opportunity for wind
: drift and other environmental anomalies.

A common belief, but it doesn't prove out in reality.  Competitive
shooters would rather have a cartridge that is more accurate even if
the bullets leave the barrel 100 fps slower.  The difference in wind
drift is overcome by the smaller cartridge shooting much smaller groups.
The '06 can shoot a 190 gr. about 100 fps faster than a .308.  That gives
a one-half inch deflection advantage per MPH of crosswind at 1000 yards.
In real deflection, it's 9 inches for the .308 versus 8.5 inches for the
.30-06.   With the best '06 match rifles shooting about 13-inch groups at
that range, their size opens up horizontally to about 30 inches with a
crosswind varying +/- one MPH.  The best .308 rifles at 1000 yards
shoot about 7-inch groups.  Those would increase horizontally to about
25 inches with the same crosswind variance.  So, the increased velocity
of a .30-06 is in reality not an advantage compared to the .308 Win.
However, given equally accurate cartridges, less wind deflection of
one over the other would be an advantage.

In the '50s , when the .30-06 was the only cartridge allowed in highpower
competition for most matches, the best of 'em would shoot 5- to 6-inch
groups at 600 yards.  The target used at 600 yards had a 12-inch V-ring
inside the 20-inch 5-ring.  Shooting possible scores at 600 yards was
an every day thing.  Then along came the .308 Win. and folks immediately
found out that in equal quality rifles, that new cartridge would shoot
groups half the size as the venerable '06.  Scores instantly became much
higher and a few years later the target's scoring ring sizes were made
smaller.  It was attributed to the .308's shorter and smaller powder
charge.  Perhaps other things helped too, but it all boils down to the
fact that the .308 Win. has better accuracy at all ranges through 1000
yards.

Outside of competitive shooting, the difference between these two
cartridges is miniscule.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Inherent accuracy of different calibres
Organization: Hewlett-Packard Fort Collins Site

C. Daniel Myers (myersc@ucs.orst.edu) wrote:

: I keep hearing how .308 Win is more accurate than .30-06 Springfield.
: Is this true?

Yes it is true.  The .308's improved accuracy is why the NRA reduced the
scoring ring sizes on highpower competiton 200 and 300 yard targets in 1966.
And the 1000-yard target's scoring ring sizes were made smaller in 1971.

Reasons why the .308 Win. is more accurate than the .30-06 are primarily
due to its smaller (lighter weight) powder charge:

  * Being the same diameter, but shorter in length, it ignites and burns
    more uniformly.  This results in smaller velocity spreads which means
    vertical shot stringing is smaller.  Tests in the early 1960s showed
    the .308s cut vertical group size about in half over the .30-06.

  * As the smaller charge causes the front slope of the pressure curve to
    not rise as fast, the bullet is pushed more gently into the throat/leade.
    This causes less bullet deformation which results in the bullet being
    less unbalanced as it leaves the barrel.  More balanced bullets shoot
    more accurately than less balanced ones.

  * Another reason is barrel twist.  .30-06 barrels standardized on a 1:10
    twist in the early 1900s.  That is way too fast for best accuracy with
    150 to 180 grain bullets they mostly used.  A 1:12 twist would have been
    much better but folks didn't understand that at the time.  With the .308
    having 1:12 or 1:11 twists, their slower-velocity bullets were perfectly
    stabilized and they shot smaller groups.  Only with 200-grain bullets
    did the .30-06 hold its own, but they had to shot with maximum charges
    and that meant recoil started getting difficult to consistantly manage.

The best 600-yard groups competition .30-06es got in the 1960s was about
5 to 6 inches for twenty shots.  As the .308 Win. cut that in half, the
bigger matches would have the top five or so competitor's with the same
perfect scores; tie breaking became a nusiance.  With a few people having
a score of 100-20V, the NRA's  tie-breaking rules didn't work; match
sponsors had to share awards between two tieing scores.

On those old military targets, the B target used at 600 yards had a 20-inch
5-ring and its V-ring inside was 12-inches.  Putting 20 record shots inside
the V-ring happend once in a while.  But the 1966 decimal midrange (MR)
target has a 12-inch 10-ring with a 6-inch X-ring inside of it.  Now, the
discrimination between scores and competitors is much easier to make.  Yes,
perfect scores are still shot on the new target; the record is 200-19X.

But in the pursuit of game animals, the differences are rather small when
sporting rifles are used.

BB