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REMOVING CASE PEENED LIP EDGE
By Wayne McLerran
Updated: 5/8/16

The following should be of interest to those that clean brass in a tumbler with
either ceramic or stainless pin media and find that the process results in a thicker
case lip or edge that shortens the case length and may interfere with the normal
loading procedure and/or when chambering a round.  
Lip peening is a common
problem if the cases are frequently annealed.  
The thicker lip is the result of the
edge being flattened and rolled over, mostly to the inside of the case, due
to “peening” when the thin edge bangs against the media or other cases during
tumbling.  There are tumbling techniques that minimize or may even eliminate the
peening, which are not the subject of this article.  For much more details on the
effects of tumbling, see the article titled,
CASE CLEANING - ULTRASONIC
VS TUMBLER WITH CERAMIC MEDIA & STAINLESS STEEL PINS.

To date I’ve experimented with three techniques to remove the edge with varying
results.  The most obvious is to shave off the rolled over lip with a tapered inside
deburring tool.  But to continue to do so will shorten the case.  If the brass is for
.40 or .45 caliber rounds the appropriate Tim Smith-Lyons case stretcher will
remove (iron out) the edge and lengthen the case if desired, but the process is
slow and la
bor intensive.  By far the best method I’ve tried is to use a pin gauge
when full length or neck resizing the brass.  I can’t take credit for the idea.  I was
made aware of the technique by Larry Bryant (aka Kokomokid) while attending a
Texas State BPCR Championship match.  Since then I’ve verified it works great.

A pin gauge or hard steel rod of the appropriate diameter is inserted in the case
prior to resizing.  When the case is resized the edge is squeezed between the
gauge and the resizing die, essentially swaging out the thick edge.  The correct
diameter of the gauge will be determined by the inside neck diameter (ID) of your
resizing die and the normal case wall thickness.  It may require some “trial and
error” attempts to determine the correct diameter gauge.  For example, let’s use
my Remington reformed .40-65 cases and Lyman neck sizing die.  The neck ID
of the die is 0.425” and the case walls average 0.010” (0.020” inclusive).  
Therefore the maximum diameter of the pin gauge would be 0.405”, but allowing
some room for variations in case wall thickness, I’ve found that 0.403” is the
optimum diameter gauge with my brass.  

Although the standard length of a pin gauge is 2”, which is ideal for .45-70 cases

or brass reformed from .45-70 cases, longer gauges can be purchased.  It’s a good
bet that most of you reading this are not machinist and are not likely to have a set
of pin gauges.  In that case individual gauges are available from several suppliers
or a machinist can make a hardened steel rod of the correct diameter.  I was
fortunate to have a 0.403” diameter drill bit that worked along with a Lyman
resizing die that allowed inserting the shank of the bit through the top of the die
prior to raising the case into the die.  But the drill bit is not ideal and I will be
buying a 0.403” pin gauge.

Update
After posting the above article I was informed of another very similar technique
used by a fellow with the handle of Montana Charlie (aka Charlie Maxwell).  
Charlie developed the Kal-Max case stretcher and is a well know contributor to
several of the BPCR and single-shot rifle forums.  Following is his process for
removing the peened edge on .45-70 brass.  Also note his technique allowing use
of the same die with longer cases.

==================================
From Charlie Maxwell:

"I use a Lee 45-70 factory crimp die, but I don't use it to make a crimp.  Instead, I
run the case mouth up almost into the 'collet', and then insert a 0.460" expander
plug into the mouth.  As I bring the ram to the top of the stroke, the 'collet'
presses the mouth rim against the 0.460" 'anvil', and the lip is straightened out.
"

"The die is adjusted in the press so that this is done with very, very light pressure
against the case wall, and leaves no mark on the outside of the mouth.  I don't get
a lip on all of the cases in a batch, so I use that 0.460" expander plug to see
which mouths resist insertion ... and just do those.
"

"By slipping (encircling) a 0.3" long ring (tube) over a case prior to inserting the
case into the die, I can make the 45-70 die work on 45-90 cases.  A longer ring
will work for longer cases.
"
==================================

So there you have it, two
very similar techniques to quickly get rid of the thick
peened edge without shortening the case.


Wishing you great shooting,
Wayne