Nerdy Technical Question On Neck Turning

[griffin ordway]

My mantra, and ongoing obsession, is "Eliminate Variables" in reloading. My current goal is to make my 300 PRC a solid 1/4" shooter. One of the variables I am seeing is that the neck thickness on my Lapua brass is very inconsistent, thus leading to inconsistent neck tension. I would like to start turning necks on my brass, but my pea brain is not understanding the process and the math involved.
I would be going with a 21st Century neck turning lathe. They state on their website that the neck turning arbor is .0002 under the bullet diameter, which for Berger 215's is .307. Now, if I size the necks down with a bushing first, they will not fit over the arbor. If I don't size them down first, they won't even make contact with the arbor, and will be too loose to turn. Another option is to size them down first with a bushing, then run an expander mandrel. of say .305 to get them to the ID that I want for neck tension, but again, they would not fit over the arbor to turn them. With only one option for the arbor diameter, I don't understand how this would work, at least without resizing the neck down, then up, too many times per loading to make any sense. Hopefully you're understanding what I am getting at (and obviously not understanding at all). Been reloading for many a decade, but have never committed to a project like this, and have never neck turned before. What am I missing? Thanks in advance.

 

[Coyote Shadow Tracker]

My mantra, and ongoing obsession, is "Eliminate Variables" in reloading. My current goal is to make my 300 PRC a solid 1/4" shooter. One of the variables I am seeing is that the neck thickness on my Lapua brass is very inconsistent, thus leading to inconsistent neck tension. I would like to start turning necks on my brass, but my pea brain is not understanding the process and the math involved.
I would be going with a 21st Century neck turning lathe. They state on their website that the neck turning arbor is .0002 under the bullet diameter, which for Berger 215's is .307. Now, if I size the necks down with a bushing first, they will not fit over the arbor. If I don't size them down first, they won't even make contact with the arbor, and will be too loose to turn. Another option is to size them down first with a bushing, then run an expander mandrel. of say .305 to get them to the ID that I want for neck tension, but again, they would not fit over the arbor to turn them. With only one option for the arbor diameter, I don't understand how this would work, at least without resizing the neck down, then up, too many times per loading to make any sense. Hopefully you're understanding what I am getting at (and obviously not understanding at all). Been reloading for many a decade, but have never committed to a project like this, and have never neck turned before. What am I missing? Thanks in advance.

Griffin
Hope that you and your family are doing well.
"Griffin" is the name of our famous CAT living with us so good choice with a name.
Neck Turning is very conferential to say the least. Some say YES and others say NO WAY.
If you are going to do this, you need to know a LOT of info and be able to spend a lot of time.
Before you go with this and spend $$$ know all the pros and cons.
Your 300 PRC may not get to 1/4" moa just from Neck Turning.
DM me if you want to know more and we can talk, but you should see what answers/replies you get from this post first.
Thanks
Len & Jill

 

[Phil Rizzo]

In sizing the necks to fit the turning mandrel, i would definitely use an expander mandrel after a bushing, for obvious reasons. 21st century can help you but have a ball micrometer handy to measure neck wall thickness when you get them on the phone. You will likely have to use a larger mandrel size by a half thou, at least, to offset springback, to get a fit on the turning mandrel.

You want to attempt to push imperfections to the outside as much as possible, for the cutter to remove. Annealing ahead of this will help, and is certainly necessary with work hardened brass.

What do your fired neck OD's measure compared to loaded OD? Removing material can help here to get a clean release, if it is necessary..
4-5 thou difference is usually fine, indicating 2-2.5 per opposite sides.

I've used a tight neck chamber before, it's not a bad idea, but there is work involved for certain. The approach I would use is to seek uniform neck wall thickness, within reason, removing as little material as possible to get there.

That along with 99 other considerations, processes and adjustments, constellation alignments etc may get you some 1/4 moa groups. Dont be discouraged if some days yield 3/8. After all, the guns used to do what you are attempting usually weigh double or more what yours likely does, and have about 1/3 the horsepower. And it is for a reason.

I understand and appreciate eliminating variables as well. If your gun is a consistent 1/2 moa or less now, I'm anxious to see the result. An arbor press (gauged) is the way to seat bullets and check uniformity of neck tension. Outliers can be culled here as well. This is after you sort bullets and cases on the front end…!

Let the hunt commence!

 

[Tiny Tim]

Agree with others. There are many things to consider, and if neck turning is desired, often a custom chamber reamer is in order to extract the benefits of doing so.

But as to your question. You will need an expander mandrel to expand the case neck to the proper size for your neck turning cutter's pilot/mandrel. So you size the case (which pushes inconsistencies to the inside of the case neck), expand the neck with the appropriately sized expander mandrel (to remove play from the turning mandrel and push irregularities to the outside of the neck), turn, and resize with either a different neck sizing bushing or resize and expand with the a mandrel to produce the desired interference fit to the bullet (which most refer to as "neck tension").

If you have your heart set on this tedious process and do not have a custom chamber, do not fully clean up the necks, only do 75-80%. I know it sounds counter intuitive, but doing otherwise runs the risk of removing to much material and the end result may be worse than when you began. In this case, a 75-80% clean-up gives the benefit of "more consistent" wall thickness without the danger of too thin wall thickness and excessive clearance in the chamber neck which results in even more work hardening of your brass.

 

[AZShooter]

There is another consideration that you should take into account. Turning necks for a SAMMI spec chamber neck might cause short neck life. Expansion and resizing for the thinner necks can cause overworking and splitting. I know I did it early on till I had a custom reamer made with a reduced neck diameter. I suppose annealing with every firing might prevent it. I also will be watching to hear about your results.

 

[nksmfamjp]

Typically, a company sells an expander specifically to fit necks to the turning mandrel.

The process is typically fl size, them expand, then turn, then size again before reloading

The value of neck turning is in fit to chamber and consistent release of bullet. I had a Savage that gave me 0.1" in group size. I had 2 other guns that needed it to improve bullet release clearance. No group improvement.

Lapua neck inconsistency really isn't a thing. What are you measuring with your ball mic?

Also, are your Bergers 0.307"? I doubt Berger has ever made a bullet that small.

 

[BRADMOTO]

My mantra, and ongoing obsession, is "Eliminate Variables" in reloading.

Make sure to be as obsessed about:
Reading wind speed & direction
Knowing the POI changes between shooting multiple positions
Knowing how atmospherics effect POI

or the obsession & effort in this category will be for not if you miss the target completely.

...and don't use too acute an angle on the reamer cutter:

 

[MagnumManiac]

I use the 21st Century turning kits.
The arbour is .002" under bullet diameter with +/- .0002" tolerance.
So, your sizing die would be .306", your bushing die will also end up at .306" and all is well.
What you are forgetting is that your chamber neck dimension may already be large, turning will NOT help you, it will make things worse.
You could attempt skim turning to remove high spots after running through your mandrel, but, unless it's a custom chamber, you're just removing brass for no return.
I turn my necks, but, I run custom chambers with .003" neck clearance and only one of them is a neck turn only chamber due to brass choice, not chamber choice.

Cheers.

 

[Varmint Hunter]

Is neck turning necessary? Many competitive shooters do not neck turn. I neck turned for a long time and had several tight neck chambered rifles. Eventually, I found that using quality brass and a no-neck turn chamber was just as good for my needs.

If your Lapua cases are inconsistent, maybe try a different brand of quality brass and you can avoid turning all together. If it works out, you'll have saved yourself a lot of work and avoided a few headaches.

BTW - true 1/4moa hunting rifles are far and few between. They are also unnecessary when you consider the multitude of variable that will affect your POI in a real-life hunting scenario. The 1/4moa is easily lost in the sauce.

 

[griffin ordway]

Typically, a company sells an expander specifically to fit necks to the turning mandrel.

The process is typically fl size, them expand, then turn, then size again before reloading

The value of neck turning is in fit to chamber and consistent release of bullet. I had a Savage that gave me 0.1" in group size. I had 2 other guns that needed it to improve bullet release clearance. No group improvement.

Lapua neck inconsistency really isn't a thing. What are you measuring with your ball mic?

Also, are your Bergers 0.307"? I doubt Berger has ever made a bullet that small.

In answer to your two questions: Yes on the ball mic. It is on a "stand" of sorts, not hand held, and is very stable. The .307 diameter of the Bergers is actual, measured diameter, on Starret calipers.

 

[griffin ordway]

Is neck turning necessary? Many competitive shooters do not neck turn. I neck turned for a long time and had several tight neck chambered rifles. Eventually, I found that using quality and a no-neck turn chamber was just as good for my needs.

If your Lapua cases are inconsistent, maybe try a different brand of quality brass and you can avoid turning all together. If it works out, you'll have saved yourself a lot of work and avoided a few headaches.

BTW - true 1/4moa hunting rifles are far and few between. They are also unnecessary when you consider the multitude of variable that will affect your POI in a real-life hunting scenario. The 1/4moa is easily lost in the sauce.

I am beginning to see that neck turning may not be the answer, and I may have been too hasty thinking it was. There are many other variables that I can eliminate before going down that path, as most here have pointed out. As for this being a hunting rifle, it's not. It is my "project rifle". I may hunt with it at some point, just for fun, but really, the whole project is just me being me, and enjoying the process of trying to build a 1/4" gun. Hell, the truth is that I may never get there, but I will enjoy the attempt.

 

[K.E.C. Darkside]

If your wanting Match Grade Precision.
You need a Match Grade Precision Chamber and Rifle, as mentioned above.
I just started turning necks for my Wildcats, because of donuts forming from moving more brass then so called normal amounts.
You have to know your chamber diamention as mentioned.
Hope this helps.

 

[MarkInPA]

May be a little off topic. Just because I was curious of the process, I tried neck turning a few cases on my Forster trimmer. Didn't turn out so good. Probably because I didn't have the neck sized for the pilot. I had considered doing a skim cut at one time just to try and uniform the neck thickness but never pursued it. Mostly because I don't have a custom cut chamber and doubted that I would ever see the benefit.

Getting a factory, hunting rifle to shoot 1/4" MOA is no easy task. I get the drive to try and make your rifle shoot as small as it can. I'm the same way and enjoy the challenge of trying to solve the puzzle. Without mentioning names, I have what I consider to be a good factory rifle and the best that I am able to do so far is 5 shot groups at 3/4" MOA. I am pleased with that. For my hunting it is more than adequate but, my hobby is to try and improve that. That's why I hang out here on this forum. Just listening and trying to learn from others.

You may be just as far ahead to try the following measuring device to sort your brass instead of trying to uniform your case necks.

REDDING CASE NECK GAUGE

 

[BRADMOTO]

I am beginning to see that neck turning may not be the answer, and I may have been too hasty thinking it was. There are many other variables that I can eliminate before going down that path, as most here have pointed out. As for this being a hunting rifle, it's not. It is my "project rifle". I may hunt with it at some point, just for fun, but really, the whole project is just me being me, and enjoying the process of trying to build a 1/4" gun. Hell, the truth is that I may never get there, but I will enjoy the attempt.

It can be done!