Re: Standard primers versus match and BR prmers
Bart Bobbitt 1993:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">From:
[email protected] (Bart Bobbitt)
Subject: Re: [RELOADING] What makes Bench Rest Primers special?
Organization: Hewlett-Packard Fort Collins Site
`Benchrest' primers are typically more uniform in their ignition
characteristics than `standard' primers. The process of mixing the
lead styphnate (the explosive), glass frit (the microscopic glass
particles that act as micro-anvils for the styphnate to compress
against) and a couple of other things is a kind of `black magic.'
About two quarts of this priming mixture is mixed together for each
lot of primers. Getting the mixture homogenous (uniform percentages)
throughout the gooey mixture is difficult. This mixture is spread
on a plate with little recesses in it that are the shape of the
primer pellet. Getting exactly the same amount in each little round,
deep hole is also a type of `black magic.' The mixture is much like
putty and a large putty-knife like tool is used to force the mixture
into each hole where it's left to dry. Then the dried primer pellets
are punched out and put in primer cups, topped with a sealer, and
finally the three-legged anvil is pressed in place.
Interestingly enough, some folks do a better job of mixing and spreading
the mixture than others. Within each lot of several thousand primers,
there's bound to be differences in the ignition characteristics from one
primer to the next. As more care is needed to make `uniform' primers,
they usually cost more.
By uniformity, I mean the consistancy of velocity they produce. Velocity
tests of the bullet is about the best test of primer uniformity. Some
very uniform lots of primers will produce a velocity spread of only 15 fps.
At the other end of the spectrum are primers that produce velocity spreads
of 100 fps, or more. Some folks have tested primer uniformity by shooting
BBs from a primed case (no powder) in a 17 caliber barrel; primers that
produce low velocity spreads with BBs do the same with powder and bullets.
Uniform primers tend to produce more uniform pressure curves, too.
Alas, not all the `benchrest' primers are as good as they're marketed to
be. Many times a standard primer will be more uniform than benchrest ones.
And some makes of benchrest primers aren't as uniform as another make of
standard primer. Even some standard primer brands are more uniform than
any benchrest brand. Some benchrest primers are hotter than their standard
versions for the same make.
In many accuracy situations, a milder, standard primer will produce better
groups than a hotter benchrest primer.
BB
</div></div>
The post that drew my attention to Bart in 1997:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">From: Joe Dioso (
[email protected])
Subject: Bart Bobbitt: 20-shot 3.325" group at 800 yards
Newsgroups: rec.guns
Date: 1997/05/10
Leafing through my copy of the May 1997 issue of Precision Shooting, I
encountered an ad for Krieger Barrels, Inc. that showed an actual-size
copy of a 20-shot group shot at 800 yards by "Bert Bobbit [sic] with
his Krieger Barrelled PALMA rifle." Now this group has a .942" mean
radius, with an extreme spread of 3.325. If it were a 5-shot group,
you'd say, "Somebody else has shot that well at 1,000 yards." But a
20-shot group? God!! </div></div>
I believe this is the group he shot 
