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Neck Turning in the Lathe

Below are photos of a method of neck turning brass if you happen to own a good lathe. This is a method very similar to Jackie Schmidt's article in the NBRSA News.

The first step is to set up a piece of .375" drill rod in a three jaw chuck. Turn this down until you get a short section with the diameter that you want to use for your mandrel. In my case, I have turned it for a .2430 diameter as I am neck turning brass for a 6 PPC. You will need to use a high speed steel or cobalt tool in order to make the mandrel. Carbide won't work as well as it deflects slightly. When you have it turned almost to the diameter that you want, file a taper on the end of the mandrel. Then polish the last few ten thousandths off with 600 grit sandpaper until the mandrel mikes .2430 using a 1" micrometer. Check the runout of the mandrel with a .0001" test indicator. The mandrel should have zero runout after you have it machined. If it doesn't have zero runout, you want to remachine a mandrel until it does. If you can't obtain zero runout, then you don't want to neck turn on your lathe as the headstock bearings may not be good enough to do it. Your mandrel should look similar to the below photo.

The second photo above shows the set up to turn necks. I use a .308 shellholder to push the .220 Russian case onto the mandrel. The shellholder is held with an extra ram that I had from a Rockchucker press with the end turned down to fit in a drill chuck. The case can be pushed on without prior expanding up to 6mm or can be expanded up prior to neck turning in a separate step as long as the newly turned mandrel will hold the neck tight while turning.

You push the case onto the mandrel with the .308 shellholder. The .308 shellholder fits loose enough that you can remove pressure from the tailstock and let the case spin with the lathe without having to remove it from the shellholder. With the carriage feed make a quick pass to the neck/shoulder junction of the case. Then engage the carriage power feed feeding towards the headstock. Check the neck diameter with a 1" micrometer and make adjustments to the depth of the cutting tool with the carriage until the turned neck still on the mandrel mikes the diameter that you want on the outside of the neck. In my case, I am turning to a .2600" neck diameter to fit in a .262 neck diameter. When you reach the diameter that you want, lock the crossfeed and compound so that they will not move and recheck your dimensions with another case. Once you reach the dimensions that you want with everything locked, you are ready to neck turn all the cases that you intend to do.

Below is a photo of the case before neck turning showing the geometry of the tool used to turn the neck.

Above is a photo showing the tool after moving the carriage to the neck/shoulder junction. Notice that the cut is pretty rough at the front of the neck and as the carriage has slowed down as I was closer to the shoulder, the cut is smoother. This doesn't make any difference as the main cut is applied with power feed as soon as the cutting tool reaches the neck shoulder junction.

Below is a photo showing the finish turned neck still on the mandrel.

Turn the tailstock out removing the case from the mandrel. Check the neck wall thickness periodically with a ball mike to make sure that it is what you want. It takes me about 2 hours to neck turn 100 cases.



Bryant Custom Precision Riflesmithing  
Bryant Custom Precision Riflesmithing