From: Lou Boyd <boyd@apt0.sao.arizona.edu>
Newsgroups: rec.guns
Subject: Re: What's a  Fat Mc?
Date: 31 Jan 1996 08:22:19 -0500

#Whats a "borerider" bullet?

In most modern small arms the bullet diameter is close to the groove diameter
of the barrel. When the bullet is fired, the barrel lands engrave the sides
of the bullet.  In a borerider bullet most of the bullet lenght is close to 
the same diameter as the bore (not the grooves) so the bullet slides down 
the barrel with only a small area at the back of the bullet being engraved
to provide the gas seal.  The reason this is popular with 50 cal bencrest 
shooters is that (in theory) the less the bullet is distorted and the more
accurately it is centered in the barrel the more accurate it will be. The
50 cal benchrest shooters have been having good success.

Borerider bullets can be shot from conventional chambers, but for best
results the chambers are specially made with very short throats so that
the driving band (the portion to be engraved) is very near the lands
and bullet is well seated into the bore before firing.  This requires
very tight control over the match between the bore and the bullet
diameter to allow the cartridge to be loaded without pushing the bullet
into the case or having it too loose.  Another problem with boreriders
is that because of the small engraving area, the bullet material must
be strong enough to spin the bullet without stripping the driving
band.  Usually bore rider bullets are solids, made of hard copper,
bronze, leaded brass, or soft steel.  Good results are being obtained
with steel coated with moly disulfide.  Barrel life isn't spectacular
but that's not the objective. Accuracy is.  The concept of boreriders
isn't new.  To some extent the minneball (sp?)could be considered a
borerider and many artillary projectiles have used this concept.