Tuesday, January 26, 2016

A problem at the reloading bench

9mm Parabellum with 4.5 grains of Unique powder on the left.  9mm Parabellum with about 3.0 grains of Unique on the right.
All the standard disclaimers:  "Safe in my gun might not be in yours yada, yada."  My plinker load is Crown Bullet's 125 grain cast round nose, 4.5 grains Unique and a COAL of 1.145"

I was reloading some 9mm Parabellum (aka, 9mm Luger) when I ran into a problem I had never encountered before.
This is a Lee Precision Powder Measure and is nearly identical to the one I have.

My procedure is to set up my powder measure, verify the weight of the powder dropped and then start loading.  I load one-at-a-time.  I drop the powder, visually inspect the powder level, place the bullet on top of the case and then seat it.  Single piece processing greatly reduces the possibility of a double measure of powder.

As noted in an earlier post, Unique is a powder that is subject to settling.  That means that each shell casing will look a little bit different with regard to how far up the sides the powder charge reaches.

When suddenly I noticed....a short charge.  My procedure is to dump the short charge back into the hopper and re-throw the charge because the most likely cause is powder bridging or lack of tapping.  The second and third throws were also short.  What the heck!

The black plastic bottom of the hopper can rotate relative to the red plastic storage bin.


This rotation feature opens and shuts a valve to make it easy to empty remnants of powder when switching loads.  This shows the valve completely open.
This photo shows the valve almost  closed.
After trouble-shooting the set-up I found that the hopper had drifted and was choking off the flow of powder to the measuring drum.  That was easy enough to fix.  I threw a piece of orange tape on the box of finished shells to identify them as suspect and went back to reloading.

PFMEA


Process Failure Modes and Effects Analysis has a very cynical view of human inspection.

PFMEA is a structured quality methodology that marries the intuition of humans with the ruthless efficiency of mathematics.  "Experts" (plural) create a list of every possible thing that can go wrong with a process.  As we have seen with my little reloading problem, this is a dynamic, living list.
Different industries will have different "scoring" but this one is pretty typical.  The main point is that 100% manual is given a "6", or 600% greater of passing a defect than "almost absolute certainty that defect will be caught".
Inspection methods are put into place to protect the customers.  Based on history, often painful history, each detection method is given a rating.  In the case of my reloading problem, I am not absolutely, 100% sure that I caught the first one.

Each "failure mode" is evaluated for its impact on the customer.  Each impact is given a severity rating.  In the case of a short charge, consequences could range from the bullet getting stuck in the barrel (very bad when the next round is fired) to not enough zip to cycle the action (that is why we practice "clearing drills").

History, as best as can be remembered, is reviewed and an attempt is made to determine how often each failure mode happens.  That frequency is also given a rating.  These frequency ratings tend to change a lot as detection methods improve.  More than one "once in a blue moon" problem was found to occur several times a day, in short spurts after better detection was implemented.

The three numbers are multiplied together to create an overall risk score.  Risk is the interaction of severity, frequency and likelihood of escape.

Detection


The first generation of living with and incorporating PFMEA into your process revolves around improving detection.

I opted for a form of double-inspection.  I am already looking at the output (the product).  I already noted that the inspections are ambiguous due to settling.  The rational response is to make the process more visual.

This is what I did.

If you look closely at this picture you will notice a strip of masking tape on the right side of the black plastic piece.  The valve is completely open when the strip of tape aligns with the screw on the left side of the hopper.  This photo shows the valve completely closed.  I will be able to ascertain the condition of the valve without having to "break down" my set-up.
Further, I intend to start the practice of placing the hopper on the powder measure assembly so the strip of tape is facing me.  Then it will be right in my face.  Either the screw will be aligned with the strip of tape or it will not be aligned.  The truly anal will add as second strip of tape to the red hopper to eliminate the possibility of the screw not being obvious enough.

I, being anal, will do that but I will use a paint pencil because tape can peel off.

4 comments:

  1. Not much of a reloader (or a gun guy, for that matter), but I was wondering if you could weigh each shell to verify the load, or if it's too small a difference.

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    Replies
    1. I think it will be too small of a difference given that I am using mixed brass and cast bullets. A fully loaded 9mm cartridge weighs about 180 grains and I am looking for a 4.5 grain shortage.

      Another issue is that my scale is a balance beam scale and it only goes up to 100 grains.

      I may fiddle around and see if three grains of Unique pushes the cast bullet out of the end of the barrel. I am 95% certain that it will.

      Thanks for writing.

      Delete
    2. Thanks for the explanation. I always find your blog interesting.

      Delete
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