HB-9 updated text (PDF) - Corbin Bullet Swaging

tween half and one thousandth, depending on whether it is an Auto-loader
or not—some pistols have a problem with slightly larger bullets which
bulge the case and cause feeding failures).
On the other hand, if I had a bullet that shot well in a given gun, I
couldn’t care less if the bullet was undersized, lopsided and backward!
The goal is to hit where you aim, and if the bullet does that, forget about
what it ought to be and just be happy that it works so well. Some armchair
ballisticians tend to wind themselves up so tightly in their theories
that they miss the fun and the point of it all: shooting. If it works, it must
be right by definition.
Many factory barrels of the same caliber are far different from each
other in diameter. The differences in bore diameter at various points even
in the same barrel can be far more than the wildest tolerances in any
bullet. Since the whole idea of controlling bullet diameter and tolerance
is to make it fit into the bore, or the rifling grooves, there’s a problem
here!
Why worry about an overly precise bullet diameter if the bore isn’t at
least that precise? We’ve had clients send us sample bullets, pushed through
a factory barrel, that came out as much as .41 caliber from a .40 caliber
pistol! In one instance, the client sent the gun back twice and got two
different oversized barrels, both different by as much as 0.005 inches
from each other. I won’t mention the gun-maker, but it is a respected
name and the problem isn’t unique.
This doesn’t mean that it isn’t important to have good control over
bullet diameter. It merely means that you should not take the “published
specifications” for granted. Measure your gun if you really want to specify
the bullet correctly to fit it. If you don’t know how to measure it, you can
fire a low velocity slug through it and capture the slug in water, and send
us the slug to measure. By low velocity, I mean just enough pressure to
get it out of the barrel reliably.
Measuring a barrel is an art. Firing the bullet through it only gives
you an idea of the diameter at the point where the bullet came out. Suppose
your barrel has “waves” in the bore, where it varies 0.002 inches
larger than the average, but the muzzle is actually tight at 0.001 smaller
than the standard specifications. The bullet might expand when it passed
through the big areas, but it would be drawn down again when it hit the
tight spots. Which dimension is really the size of your bore? Who knows—
it all depends on your meaning. Average? Mean? Tightest point? Loosest
point? Standard deviation?
You want a bullet to fit so it won’t be distorted and so powder gas
won’t escape around it and cut the jacket or lead like a torch. It’s worse to
have gas jetting around the bullet in the loose places than it is to have the
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