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Subject: Re: Testing .308 Win. Handloads
Organization: AT&T

From article <>, by
(Bart Bobbitt):

# In January, 1995, New Zealand hosts the International Palma Matches.
# Their national shooting organization will provide .308 Win. ammunition
# loaded with the following components:
#   * Sierra 155-gr. Palma Match bullet seated to OAL of 2.800 +/- .002-in.
#   * 45.3 grains of Hodgdon H4895 (Australian manufacture).
#  Here's the velocity numbers vs. shoulder pressure of
# heavier (H), meduim (M) and lighter (L) amounts:
	average		vel. loss	recoil weight

    L    3019		-29.2		6 lbs
    M    3033		-15.2		11.5
    H    3043.6		-4.6		37

The standard deviation of the mean for each group came out to less than
1 fps if I am right, so it is clear that the trend is significant.
What an excellent experiment.  We should be able to estimate the
weight of Mr. Bobbitt's shoulder from this.

From conservation of momentum the sum of the bullet and powder gas
momentum should equal the recoiling gun momentum.  Then we can figure
the energy of the recoiling gun and figure the amount of velocity lost
from the bullet due to this  dE=m*v*dv.   Then we must add the velocity
of the recoiling gun to this (even greater component) to get the total
velocity loss to recoil.  Using  a value of 5000 fps for the vel of the
powder gases, the above table shows the velocity loss due to recoil
and the corresponding recoil weight (gun plus shoulder).

If the gun weighs about 6 lbs and the light (L) shoulder pressure adds
no additional recoil weight, we get the 3019 which is 29 fps less than
if the gun were fixed with no recoil.
The medium (M) shoulder pressure adding an effective 6 lbs, accounts
for the 15 fps loss, and finally with the full shoulder weight of
around 30 lbs, the velocity loss is limited to 4.6 fps.
Truly a heavy weight shooter :^).


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