From: toby@stein.u.washington.edu (Toby Bradshaw)
Subject: Re: Wanted: .308 varmint bullet suggestions
Organization: University of Washington, Seattle

In article <9302021724.AA01304@hpfcls.fc.hp.com> ses@hpfcls.fc.hp.com (Steve Speer) writes:
#It seems
#unreasonable to think that the center of the hole to the center of the hole
#could be measured accurately enough to report accuracy to the thousandth of
#an inch (I guess you could measure to the outside, then subtract one bullet
#diameter, is this what is done?).

Not exactly.  A target measuring caliper is fitted with a plexiglas
plate that has several circles conforming to the diameter of commonly
used target bullets.  The widest dimension of the group is determined
(sometimes by eye, sometimes measuring in several directions is
required) and the appropriate circle is placed over one of the
extreme bullet holes with the caliper set to zero.  The caliper is
pinned down with a rubber foot to stop any slippage, and opened until
the circle is covering the other extreme bullet hole.  The group size
is read directly off the caliper, and is a center-to-center measure.
Then, the target is turned upside down and the group measured the
other direction.  The measurements usually agree to within .000 to
.002, and the larger measure is taken as the group size for official
scoring.  If bullets are tipped, or are in the black part of the
target, the measurements are less accurate.  In the white part of
the target with bullets flying true, 0.001 is not out of line.
Aggregates are reported to four decimal places, and it is not
uncommon for the last digit to determine the winner.  At a big shoot,
it will generally take a group in the zeros (<0.100") to win a
5-shot match at 100 yards.

Toby Bradshaw
Department of Biochemistry and College of Forest Resources
University of Washington, Seattle
toby@u.washington.edu

From: Gale McMillan <gale@mcmfamily.com>
Newsgroups: rec.guns
Subject: Re: Record .50 BMG 1000 yard group shot in Reno.
Date: 30 Jun 1999 09:58:36 -0400

The .0001 is a result of the math of adding a number of groups. Either
5 or 10 to and then dividing by the total number of groups to get the average.
In some numbers you could carry it out to indefinite numbers so you
round it off to 4 decimals. As for measuring groups  to .001 it is
easy to do with the instruments we use and as for the reason for carrying
it out to 4 decimals. If you didn't there would be lots of ties at big
shoots where there lots of competitors . It is not uncommon for there to
be 3 or 4 shooters with the same score if you rounded it off to 2 or three
decimals. When the famous .009 group was shot it was exrayed and the negative
blown up so that the fractures in the paper could be measured then calculated
from the 500 times enlargement  out to 5 decimals and since it was
a single group it was rounded off to 3 decimals.When the actual group was
measured on a 60 power traveling microscope it measured .224. which was
the diameter of one of the bullets .If they had not measured it by blowing
up the negative the world record would have been .000 and could never have
been broken so it would have retired that record.