Neck Turning

[browninghunter86]

What is the process to determine how much to turn necks down and how do I measure the brass?

Using WW 308 win brass.

[sundog]

This is what I do, others may have a different process. First, I dedicated a batch of brass to a particular rifle - quality cases all equal in weight. Using fire formed brass it is cut to at least the thinnest measurement back to, but not including, the shoulder, making each case uniform thickness in the neck. Considerations for doing this should included chamber dimension in the neck. Since I shoot a lot of cast that is normally .001 or more over groove diameter, I want as much clearance as I can get, so I can load a larger than nominal size [cast] bullet. The first firing after neck sizing will reshape that brass once again. In most instances when neck sizing you will notice that more will be taken off one side than the other to get to uniform thickness. Again that thickness is a function of what you are trying to accomplish. The major goal is to present the bullet concentrically to the bore and assure uniform neck tension. Although the process itself is relatively simple, the reasons and concept of the process can be quite involved.

Bottom line is that a rifle that shoots well improves with various case preparation processes -- all time consuming.

[wncchester]

"What is the process to determine how much to turn necks down and how do I measure the brass?"

"The" process is whatever you wish, there's nothing established about it and what we wish varies quite a bit.

Case necks tend to be much thinner than they need to be for a standard chamber so any turning we do just makes a bad fit worse. Most of us want to avoid excessive thinning so we generally skim off an average of maybe 75% of the circumference and call that good.

We can measure neck thickness at the mouth with the jaw tips of an inexpensive dial caliper OR buy a much more costly "ball mic" micrometer. Or seat a known diameter bullet and mic the outside diameter of the neck that way. Actually, since neck thickness is not at all critical for factory chambers I no longer bother to measure turned necks. Well, except for massive case conversions or tight neck chambers that require turning to allow chambering but those are not common things.

Case brass can only stretch about 1 thou before the metal's elastic limit is exceeded. Knowing that allows us to mic the diameter of a fired case neck and add a thou and be reasonably sure that's the diameter of the chamber's neck. (It also tells us that any so called "neck tension" greater than a thou is kidding ourselves so far as bullet grip goes.)

[browninghunter86]

ok I need to measure the fired cases necks. I have a Mic that reads 0.0001". I do not have a factory chamber.

[603Country]

Measure neck thicknesses at several places on the circumference of the neck of a few cases. See if you can get a decent determination of what's the thickest and what's the thinnest that you'll find. Some folks will take off metal to get to, or near to, the thinnest measurement. Personally, I don't go all the way to the thinnest measurement I've found, but prefer to 'skin' off the high spots (it's a judgement call for me as to how much comes off). I feel like that taking metal off of 100% of the neck surface is taking too much metal off. Since I buy pretty good brass (Norma and Nosler mostly) I don't take off a lot of metal. And be careful that you don't cut into the shoulder of the cases.

I'm not a competitive shooter, so maybe those guys will have a more rigorous method of determining how much metal to remove.

[Bart B.]

Few folks really understand how a bottleneck case that headspaces on its shoulder fits the chamber when it's fired. Doesn't matter how much clearance there is between the chamber neck and case neck. They all center perfectly in the chamber neck floating in space with some clearance around the case neck to the chamber neck. Even in a .308 Win. chamber, .243 Win, .260 Rem and 7mm-08 rounds chambered in it will all have their necks well aligned in the chamber center should they be fired in it. Same thing for .25-06 and .270 Win rounds in a .30-06 chamber. These round's necks float in the middle of the chamber when the bolt's closed on many rifles and all of them when the round's fired. Rimless bottleneck rounds do not rest in the bottom of the chamber when the bolt's closed on them. Nor are they in that place when they're fired. Check out your rifles and see were all the forces come from that position a round in the chamber. It's easy to do if you just look at the hardware and know how it works.

Nor does it matter how uniform the case neck wall thickness is; less than .0015" spread's enough for excellent accuacy. It's more important that case necks be well centered on case shoulders. Full length sizing fired cases does a better job of doing this than neck only sizing.

[FrankenMauser]

I turn necks if they fall into two categories:
1. Too thick to chamber. -I turn the entire lot to a consistent thickness.

2. Wall thickness varies more than 0.002". -I turn the entire lot to the thinnest dimension encountered on any single case in the lot (unless it's an extreme outlier).


Either would generally result in a thickness of 0.014-0.015" with my .243-based 6mm wildcat, for example. That leaves me with 0.002-0.003" clearance in the chamber. That's more than many competition shooters seem to believe is ideal, but it works for me and my rifle.

[Bart B.]

FrankenMauser comments:

Either would generally result in a thickness of 0.014-0.015" with my .243-based 6mm wildcat, for example. That leaves me with 0.002-0.003" clearance in the chamber. That's more than many competition shooters seem to believe is ideal, but it works for me and my rifle.

There are competitors who feel that even .004" to .005" clearance around a 30 caliber case neck's excellent for best accuracy. They have rifles and ammo that shoot bullets from such setups that equal the accuracy of tight necked benchrest chambers. Sierra Bullets is one as their 30 caliber test barrels have that much neck clearance; they don't believe in tight necks at all and haven't since the early 1950's.

[browninghunter86]

I sorted all my Win 308 brass to 0.013-0.014" neck wall thickness. So they have 0.001 variance at most. All the others got culled out for hunting/sighters-foulers

Do I even need to neck turn? Not sure if that 0.001 will translate into anything at distance that would really be worth spending $150 to get the neck turning set up

Thanks for the help

[FrankenMauser]

0.001" isn't enough to worry about.

The neck turning tool probably has at least that much deflection while cutting, anyway.

[old roper]

Here is something from Sinclair on turning necks

http://blog.sinclairintl.com/2011/12/29/neck-turning/

[schmellba99]

I turn all of mine. Whether it actually makes any tangible difference or not is up for debate, but A) I have the tool B) it only needs to be done once and C) I dont' feel as if there is any negative benefit.

You will be surprised at the variance in the neck thickness of much of your brass. Whether or not that translates into an off center projectile is your call, but I like the idea that I'm ensuring there is no contact with the chamber wall on one side of hte brass, as well as maximizing uniform neck tension.

I only trim for a couple of calibers - my .243 I turn to .012" and my .223 I turn to .010.

If the brass is thicker (like my current batch of Winchester for my .243), I'll modify what I turn it to. Feeler gauges are great for this application.

[Bart B.]

I've reloaded WCC58 match .308 Win. brass a couple dozen times per case with necks turned to .0115". On .3082" diameter bullets, the loaded round's neck diameter is .3297". They were fired in SAAMI spec chambers with .3440" neck diameters. None had any necks split whatsoever.

Note that neck wall thickness or uniformity has nothing to do with how a .308 Win. case centers in the chamber neck when it's fired. The case shoulder's well centered in the chamber shoulder by the firing pin impact before the primer detonates, burns the powder and pushes the bullet out. If the case neck's not well centered on the case shoulder, it'll never be centered in the chamber neck.

And .001" off center of the bullet in the chamber neck or throat has zero effect on accuracy any way. Well, maybe a couple hundredths of an inch at 300 yards and one tenth of an inch at most at 600 yards. Unless you and your shooting stuff is no worse than 1/8 MOA at 100 yards, I wouldn't worry about absolute perfection in this matter anyway

[browninghunter86]

necks turned to .0115". On .3082" diameter bullets, the loaded round's neck diameter is .3297"

That # seems off. Should be 0.3312" right?

Thanks for the reply. I was just curious to see if that 0.001" would make a huge difference in relationship to the neck tension. I guess if I did I would trim to 0.013 or 0.0125". I am going to just try not turning for one year and once I gain experience I will see if the need is there to turn.

Am going to be shooting F-Class TR competition

[Bart B.]

0.3312" right?

Yes. The battery in my mental calculator was weak.

[browninghunter86]

I know how that is.

Well that is good to know about no real issues with that much clearance in the chamber. My fired brass comes out 0.3435". So I have a good bit of chamber clearance with a loaded rounds neck measuring 0.335"

[Bart B.]

Note that case necks rarely expand fully to the chamber neck. They stop short of that as the bullets already in the bore when peak pressure's reached. And gas blows powder residue back between the case and chamber necks blacking the outside of the case necks. So fired case neck outside diameter is a couple or more thousandths smaller than chamber neck diameter.

[243winxb]

Note that case necks rarely expand fully to the chamber neck.

Very true. If you use a bushing die & only size 1/2 of the neck, after 3 or 4 loading, you will get a true reading on the necks diameter.