Hello everyone. Stanley here. Many people have heard of case neck turning, but few have seen it done and even fewer have actually done it. If you are in search of extreme accuracy, case neck turning may be right up your alley.
First off, what is case neck turning? Case neck turning is when a person thins the outside of their case necks by using a tool called a neck turner.
Second, why would anyone want to thin their case necks? Case neck turning helps make the case necks have a more uniform thickness. Having a more uniform neck thickness allows the bullet to have more consistent neck tension helping to improve accuracy.
Third, who will benefit from this process? Anybody who loads their own ammunition and wants to take the next step to improve the accuracy of that ammunition.
In the video, you will see me turning the necks on 30BR brass. This brass started out as Lapua 6BR and I expanded the necks using an RCBS expanding mandrel. One of the consequences of expanding the case necks is that you may develop a donut. If you look closely at the picture below, you will see a slight bulge where the arrow is. This is the donut. When you are watching the video you will see when the turner hits this area.
I use two turners when I am working my 30 BR brass. One turner is set up to barely skim the top of the case neck then take off the donut. This first turner essential makes a smooth working surface for the second turner. The second turner, many times called a finish turner, is set to take off the desired amount of brass.
While watching the video you will notice that I lube the inside of the case neck using a Q-tip. I also (not shown in video) lube the pilot on both turners. The pilot is the part of the turner that goes into the case mouth. Lubing the pilot and case neck is very important for reducing the friction. Lubing allows the pilot to slide in and out of the case neck without “grabbing” the sides. Reducing friction also keeps the temperature of the pilot from increasing. If the temperature of the pilot increases too much it can cause the pilot to expand which then can change the depth of the cut being done. This is an accuracy killer. The lube I use is a combination of cutting oil, STP motor oil, and Imperial sizing lube.
Having the correct size pilot is vital to obtaining the best results when case neck turning. You want the O.D. of the pilot to be roughly .001 smaller than the I.D. of the case neck. In other words, you want the pilot to just slide in the case neck with very little resistance. There are a couple of ways to ensure this. One is to purchase an expander mandrel that is slightly larger than the turning pilot. The other option is to purchase different pilots and match the pilots to the case necks. I have both but I prefer the latter and have several different pilots that I can match to my cases.
There is a little bit of math involved when turning brass. If you decide to turn your case necks you will need to know what you want your overall clearance to be. For example; on this particular new batch of brass for a Kreiger 30 BR barrel I wanted roughly .003” neck clearance. My margin of error is +/- .001”. Meaning, I will not be able to tell the difference, on the target, if I have .002” to .004” clearance. (as long as all cases are the same) If I aim to have .003” clearance then that gives me some room for error. It is one thing to be able to measure .003, it is quite another for me to be able to set up my equipment to cut and get exactly .003 inch clearance.
Here is where the math comes in. My 30 BR chamber is .330”. If I want to have .003” clearance, that means I need my over bullet measurement to be .327” (.330 minus .003) The 30 caliber bullets that I am using have a pressure ring of .3086”. .327” minus .3086” = .0184”. 0184 divided by 2 (there are 2 sides to a case neck) = .0092”. I want my case necks to be around .0092” thick. That will give me a theoretical clearance of .003”.
I turned this particular box of Lapua brass down to a final measurement of around .0097”.
This should give me a theoretical clearance of around .002”. I type theoretical because the only way to be certain of your neck clearance is to measure a loaded round over the pressure ring of the bullet. Commonly called the over bullet measurement.
The actual overall bullet measurement turned out to be .3280. This gives me a clearance of .002.
Do not be overly concerned if your neck thickness and actual over bullet measurements do not add up perfectly. You are measuring a piece of brass to the .0001”. It takes only a very small error (how tight you squeeze the micrometer for example) to throw these numbers out of whack. The number that you should trust is the final one when you check the over bullet measurement with a micrometer.
Well, there you have it. A quick run-down on case neck turning. Is case neck turning for everyone? Absolutely not. Case neck turning is for a few, highly accuracy minded, hand loaders, that want to squeeze every bit of accuracy out of their ammunition. I hope you enjoyed the write-up and video. Until next time, enjoy the experience.
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Jason is a father, husband, avid outdoorsman, Benchrest shooter, and science teacher. Jason is our go-to for learning about Benchrest Shooting, loading techniques, and hunting. Feel free to ask questions in the comments, and if you like this post make sure you hit the like button.