From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: long range rifle 7mm mag
Organization: Hewlett-Packard Fort Collins Site

I (bartb@hpfcla.fc.hp.com) wrote:

: Fouling can be caused by either the powder or a rough bore.  A properly
: lapped bore won't foul.  The 4831 types of powders, although often used
: with the 7 mags, aren't as clean burning as IMR4350.  But all magnums
: tend to throw a `wild' shot once in a while.

I should clarify my comments above by stating that a properly lapped
`and smooth' bore won't foul due to bullet jacket material scraping off
and clogging the micro-valleys in the finish.  When this happens, the
bullet is immediately unbalanced.  But a powder that doesn't burn clean
for the bore size and charge weight can foul any bore.  The more fouling
there is, the more bullets will be changed, hence, unbalanced.

Any bore fouling will unbalance bullets.  And unbalanced bullets don't
shoot as accurately as balanced ones.  When bullets spin from 140,000 to
300,000 RPM (depending on velocity and twist), it doesn't take much
unbalance to cause inaccuracy.

An exception to this situation is when a bore is quite rough.  These
bores typically scrape quite a bit of jacket material off for the first
several shots.  Then the bullet jackets won't have as much material
scraped off and the barrel shoots more accurately.  Many factory barrels
are like this.  Oft times, folks will comment that their barrel needs
5 to 10 shots through it before it starts shooting accurately.  More
often than not, the bore is too rough to shoot accurately from a clean
barrel.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: long range rifle 7mm mag
Organization: Hewlett-Packard Fort Collins Site

wayne sugai (wsugai@seanews.akita.com) wrote:

: i think that a more accurate statement is that a properly lapped bore
: will foul less than otherwise, but i believe all bores will eventually
: foul, given the nature of the stuff that's going through them.

I agree that a well and properly lapped bore won't foul....with jacket
material.  But I know several highpower competitors who will shoot close
to 200 shots before cleaning and their barrels don't foul.  The barrels
shoot just as accurately after about 200 rounds as they did when starting
from a clean bore.  But they use IMR4064 powder; one of the cleanest
burning powders around.  I tested one of my own target barrels at 600
yards some years ago.  After 150 shots and no cleaning, it still shot
about one-half MOA 20-shot groups.  But I feel better if I keep the
barrel clean like after about 20 or 30 shots.  And I think barrels last
longer if cleaned regularly.

BB