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From: crs@beta.lanl.gov (Charlie Sorsby)
Newsgroups: rec.guns
Subject: Fire-forming vs. excessive case-neck length
Message-ID: <35329@mimsy.umd.edu>
Date: 6 Jun 91 19:27:42 GMT
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Approved: gun-control@cs.umd.edu

# In article <35247@mimsy.umd.edu> hes@ccvr1.cc.ncsu.edu (Henry E. Schaffer) writes:
# # Note that this is clearly in the acceptable area, but also notice
# # how little difference there is.  (The danger is that if the case
# # neck is long enough to jam into the end of the chamber, it will
# # put pressure on the bullet and hold it in after ignition.  This
# # will cause an increase in pressure within the chamber, and can
# # lead to such undesirable results as blowing up the gun!)
# 
# Henry is completely accurate in this respect, with one exception.
# Benchrest shooters (myself included) when fire-forming new brass
# will typically seat the bullet out so far that it is inserted
# into the rifling about .0005".  The bullet in the rifling and
# the base in the boltface squeeze the cartridge in much the same
# manner as the the head and tailstock in a lathe and cause the
# the cartridge to be centered in the chamber as much as is possibly.

Aren't we talking about two different things here?  It seems to me
that there is a vast difference between jamming the neck of the
case into the taper of the throat and pushing the bullet into the
rifling both as to consistency and degree of pressure increase.

What I believe Henry is describing is the effect of excessive
*case* length, not excessive overall length which can be caused by
several things including bullet seating depth.  When the case is
too long, the neck extends into the throat which is dimensioned for
the bullet, not for the case, diameter.  Thus, the case neck is
jammed, radially, into the surface of the bullet and holds it
significantly more tightly than normal--a very unsafe situation.

Best,

Charlie Sorsby						"I'm the NRA!"
	crs@lanl.gov