TexasMac's Web Site
By Wayne McLerran
Updated : 8/29/20

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 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,

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 labor intensive.  By far the best method I’ve tried is to use a pin
or plug 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.

I use a Lyman neck resizing die that allows full access to the die
chamber from the top of the die with the extractor rod removed.  A
hard steel rod of the appropriate diameter is inserted into the top of
the sizing die as the case is being inserted into the die.  As the case
enters the neck of the die it's squeezed against the rod and flattens
out the peened edge.  See the photo below.  The top portion of the
0.403" diameter drill bit is taped to protect my fingers and also is a
guide to indicate how far to insert the bit.
A slight variation of the same technique is to insert a pin gauge into
the case prior to inserting it into the sizing die, but then you'll have
to pull the gauge out of the case.  The long rod or drill bit through
the top of the die works better for me.  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 0.01
1” (0.022” inclusive).  Therefore the optimum
diameter of the pin gauge
is 0.403”.

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 or plug 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.

After initially 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 allows 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,