Trimming the Meplat on 80 grain SMK Bullets

Picture of some before and after bullets

Since I do not have a lathe but do have good collection of thin brass tubing.  My Meplat trimmer is made from a series of thin brass tubes soldiered together.  I started with a 3/8 inch inside diameter piece of brass tubing which allowed the end mill fit inside.

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On one end of the brass tubing I inserted several small pieces (about 3/4 inch long) of brass tubing which will hold the 80 grain MatchKings.  The diameter of the small tubing pieces were decreased until the 223 caliber bullet would just fit.

 
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On the other end of the brass tube I also added four small pieces of brass tubing 5/16 inch long in increasing diameter.  This increased the area on the one end for contacting the stop collar on the end mill bit.  Some of the little shaft collars I found all had a small chamber on the inside hole which required the larger area or diameter on one end of the brass tube for the collar to contact.

 
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All the small brass pieces were soldered together except the one to hold the bullet. Since I do not have a lathe or any chambering tools or reamers, however I still need a way to locate the bullet inside the brass tubing.  So some epoxy to the rescue.  With a little release agent on the bullet I cast a pocket or chamber from an 80 grain Sierra MatchKing Bullet.

 
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In order to have the bullet correctly centered and aligned within the brass tubing I wrapped the rear portion of the bullets bearing surface with some scotch tape.  About six layers of tape allowed the bullet to just fit into the brass tube and centered base of the bullet within the tube.  I then cast the front part of the chamber or pocket.  After the epoxy was cured I removed the bullet.  Then I removed the tape from the bullet.  Next I removed any release agent on the bullet and inside the brass tube cast chamber.  Then reapplied release agent to the bullet and cast the rear portion of the pocket or chamber where to tape was in the brass tube.  When the bullet is placed into the trimming holder, just the rear boat tail portion of the bullet is sticking out.  The bullet is completely supported along the bearing surface and part of the bullets nose.  A small portion of the bullets nose sticks out inside the trimmer for trimming the bullets Meplat and also allows pushing the bullet out of the pocket after trimming.

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Using this cast chamber method requires a little more effort; the bullet must be pushed in and out of the brass tube.  However this extra effort pays off later, the bullet is held tight enough to prevent spinning during the trimming operation and also hold the bullet in the correct alignment while performing the Meplat trim.

 
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I have incorporated my cordless electric screwdriver into this trimming operation. This makes the trimming process go very quickly and easy.  Just press the bullet into the holder and stick the holder on the cutter.  The bullet is held into the holder well enough to prevent spinning while cutting.  Just a small amount of pressure is required on the end of the bullet while cutting.  A small wooded stick sticking out of a little wooded block makes pushing the bullet out easy.  Pushing the bullet out while in the vertical position also allows for all of the small copper chips to fall out.  I am currently over trimming my 80 Sierra MatchKings.  I am removing about 0.037 inches from the nose of the bullet.  The first trimmer I made the bullet chamber was off centered thinking it would cut better and not rotate, wrong, bad idea, the end mill deformed the bullet a little to one side while cutting and left a burr.  Putting the bullet in the center is crucial for a good cut.  So after trimming some wrong and trimming them again and may be again I am currently at 0.037 of an inch being removed.  They seem to shoot okay so that is wear the stop is on the cutter for now.

 
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Results so far seem to indicate less vertical for me.  It is hard for me to quantify this more than saying I think so because I have been changing other things at the same.  For now I am going to keep doing it for the 600 yard space gun 80 Sierra MatchKing Ammo.

 
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The first holders I made were for a 3/8 inch diameter end mill.  However the better choice is a 3/16 inch four fluted end mill with a 3/8 inch shaft.  Since I am going to keep this trimming process going for awhile I noticed to remake the holder for the 80 grain MatchKing bullet and document the procedure for this article.  I had to dull the outside edges on the 3/8 end mill so it would not cut the inside of the brass tubing.  The 3/16 diameter end mill would be easier to get in and out of the 3/8 I. D. brass tubing and will not be affected by any of the copper chips.  The rest of my current holders may be shorten and used with the 3/16 inch diameter end mill.

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