Rebarreling and Home-Shop Machining

Renecking a Full Length Sizing Die

It is helpful when resizing rifle casings if you do not overly work the neck. This produces straighter cases and also does not work harden the brass as fast so the necks stay soft through more firings. One way to work the brass less is to use a bushing style full length or neck size die. Another way is to have a full length die renecked by the manufacturer (Forster offers this service) or to do this yourself. Precision grinding the interior neck portion of the die is described below.

Neck Size Shoulder Bump Die

A fairly new die from Hornady is their Match Grade Neck Size Shoulder Bump Die. It is only available in a few calibers like .308, and .223. Not for the 30/06. I have one in .308; it works great. I also ordered a custom neck size shoulder bump die from Hornady in 30/06 quite a while ago. It has arrive now and is a very similar dimension in the body to my home-made die.  It has replaceable neck busshings.  $75. This type of die which is in between (in body size) a neck size and full length die has been available from custom manufacturers for quite a while.

 I had a spare Lee Full Length Die. The neck size on this die is .325 inch. I size my necks with a Lee Collet die which is the equivalent of using a .334 inch bushing in a bushing die. The necks are worked as little as possible either with the collet die or the .334 bushing and the brass comes out straighter. With the .325 stock neck on the full length die the necks are worked a lot on don’t come out very straight. Fairly straight brass is essential for good accuracy. I decided to reneck this Leefull length die.

Chucking

I chucked the Lee Full length die in a four jaw chuck with the threads supported by a brass strip. I indicated in the neck with a dial indicator and a hole attachment. I moved the indicator along the length of the neck and I was still dialed in, <.0001 inch radial runout, also < .0001 inch axial misalignment. Great. Chucking previously on the outside of the cylindrical non threaded portion of the die did not work as well. I ground the inside of the neck, with the Dremel tool post grinder that I made, until it was .0005 inch less than the bushing I normally use. I will polish the rest out using a brass rod that has a slit cut with a .010 inch thick X-acto saw. I can insert a strip of fine wet or dry sand paper and spin the rod with the Dremmel and achieve a mirror finish on the interior of the bore. A little extra attention from the large end of the hole will radius and smooth out the entry to the neck. I plan to do some more work to this die, but if you like to full length size this is a way to breath new life into an old die.

Enlarging the Body of the Die

I used a couple of fired cases to lap the body of the die larger. I chucked the case in a Lee case trimmer case holder. Then I used Wheeler 350 grit paste that is available from Midway and an electric screwdriver. Lapping with an electric screwdriver at slow speed or by hand by locking the electric screwdriver worked the best. A drill motor overheated the work a bit and dries out the paste. I wetted the paste occasionally with Hoppes gun oil. Keep the paste off the neck. When the paste appears on the shoulder of the case you are done with that case. The case shrinks a bit so I used a second case to enlarge the area right next to the case shoulder which is the last part of the die to be lapped in. I quit when this second case had paste run up onto the shoulder. It takes several hours in front of the TV to finish. I checked the size of the die by cleaning it out occasionally and inserting a fired case to see how far it would go. Mark it to monitor your progress. Then I checked it more carefully 9 times by sizing an oversize case and measuring its diameter at several places along the body.

            I polished the die with 1500 grit paper on a brass rod with a slit cut in it in the small drill press at the highest speed. This can be used to polish the neck of the die as well. I followed up with Flitz metal polish on a large cotton swab that I got with my Birchwood Casey Bluing kit. These items are shown in the last photo along with the first lapping case which I have cleaned off to show the pattern.

            The case in the die in the photo shows the first contact of the case with the body of the die when inserted by hand. A very small sizing is done withthe press in the next 1/16 inch of travel. The greatest sizing will be right at the body shoulder junction on the body. This happens to be the point where the case is likely to expand when you bump the shoulder, so this is good in my opinion.

Sizing Results

I sized 9 oversize Lapua cases with unturned necks that were fired in a standard chamber Remington 30/06 rifle with the shoulder bump die. The runouts were 1 at .0015 inch one at .0005 inch and the rest .001 inch. This is outstanding for cases fired in a standard chamber. Before this modification runouts tended to be .002-.006 inch, mostly .004 due to the large amount that the necks were working. The shoulder was bumped back .0005 inch with the setting of the press that I used. The body was very near in size to a neck sized case, just a bit smaller right at the shoulder to body junction. The necks of these cases were sized to about a .002 inch interference fit with the bullet. The neck of the die ended up right at .334 inch after sanding right as intended. Lucky here. It needs to be a bit smaller for brass with thin necks. The Lapua brass is a little thicker than even Federal Brass.

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