Need guidance...case neck thickness

[birdiemc]

Folks I think everybody got a little carried away and forgot to answer what the OP wanted to know. Being clueless myself, when he said he was clueless where to start I got excited hoping to get schooled on the how and why. Like why ream the inside if the expander is supposed to push all the inconsistencies to the outside where they get turned off? A tubing micrometer tells you thickness but how do you determine if it needs to come off the inside or the outside? Why exactly do you have to have "21st Century Titanium nitrided expanders and mandrels with a carbide cutter"? How do you ensure you're sizing necks so they fit properly on a mandrel? What type of fit are we looking for here?

 

[30BR]

Folks I think everybody got a little carried away and forgot to answer what the OP wanted to know. Being clueless myself, when he said he was clueless where to start I got excited hoping to get schooled on the how and why. Like why ream the inside if the expander is supposed to push all the inconsistencies to the outside where they get turned off? A tubing micrometer tells you thickness but how do you determine if it needs to come off the inside or the outside? Why exactly do you have to have "21st Century Titanium nitrided expanders and mandrels with a carbide cutter"? How do you ensure you're sizing necks so they fit properly on a mandrel? What type of fit are we looking for here?

 

[30BR]

I am ASSUMING that this is for a std chamber; not a "tight neck" like many shoot in benchrest. All brass, even Lapua, will be uneven in thickness at the neck. You cut the necks to make that OD more uniform. Especially with a std chamber, you don't want to take too much off the neck wall thickness, because doing so means the remaining brass has to expand that much further to get a good seal upon firing. Excessive clearance will lead to premature neck cracking for that reason. So what you want to do is turn the neck just enough to take off the thickest spots.
FIRST, and VERY important, trim all the brass to exactly the same length. If you don't, your neck cutting tool is going to either cut too short, leaving some of the neck uncut near the shoulder, or it will cut some brass too far into the shoulder, weakening the case.
You next need to run the brass over an expander mandrel, to make sure it is round and opened up to PRECISELY the right ID for the cutting tool's mandrel. So you want to buy your expander mandrel and your cutter from the same company to make sure you have a perfect match.
Measure the existing brass wall thickness at 3 0r 4 spots on the neck. You want to cut that brass just so the high spots come off, not necessarily the entire circumference of the neck. (That could lead to excessive clearance.)
When you buy the tools from 21st Century, they may have many choices.
http://www.xxicsi.com/neck-turning-tool-kit.html
I like the titanium nitride because they can run without lube if you cut slowly and don't allow the tools to heat up.
You need to adjust the cutting depth so that only the high spots are taken off. Do this very slowly and measure the results. Adjust the DEPTH of cut so that the cutter just kisses the shoulder. (The reason you need the correct ANGLE on the cutter). Now lock everything down gently, and cut another piece and measure it to see if anything shifted.

Keep some ice wrapped in a towel handy so you can rest the cutting tool on it between cuts to keep it cool.

IF you had a tight neck, you would cut all the way around so that the loaded round would have about .0015" RADIAL clearance or .003" total clearance. (For example, a .262 6mm neck chamber needs the brass to be cut to about .008" thickness. .243 + .008 + .008 = .259").

Hope that helped.

By the way, many now go with "no turn " necks in benchrest because the task is so tedious, and you are better off spending your time learning how to read the wind.

And as far as inside neck reaming goes, every time I tried it, I ruined more brass than I fixed. My suggestion is don't do it. Leave THAT to the experts, who know how to remove the dreaded "donut". With a std chambering such as I described, you need not worry about a donut forming. http://www.6mmbr.com/neckturningbasics.html (note that article is about 14 years old I think...)

 

[RegionRat]

The question about how to size the case neck for trimming is an important one, especially with three way cutters.
The chamfers are not going to come out right if the case neck diameter isn't the same as when the chamfer cuts were adjusted. So, basically you pick a sizing process first, and then adjust those trimmers to that diameter. The ones like the Giraud pilot on the shoulders and the case sizing is a factor since the tool doesn't index off the over all length. Even the tools that use a pilot for trimming, work well only when the case is already sized. The pilot clearance will be more consistent and the ones that chamfer are even more picky about the case neck diameter.

Reaming a case neck does come up with some circumstances. Specifically the ones where there is flow near the shoulder to neck junction and a "doughnut" forms. This pattern doesn't happen often, but when it does you have a hard time with bullets that need to go past that junction unless you ream.

The sizing process doesn't really care about the ID or OD concept. We tend to trim necks from the OD since it is far easier than getting a reamer to finish the length of the case neck. The brass will conform to the firing and sizing process either way.

 

[sedancowboy]

Hey guys if you search on this site you will find this has already been discussed in a thread called
"Inside or Outside" It answers all the questions asked above.

 

[redleg1013]

First off you'll need a tubing micrometer, no, it doesn't need to be a Starett or Mitutoyo, but you will need some feeler gages (harbor freight will suffice), check them with a micrometer to make sure they're legit within a half thou (we're not all tool and die makers) and then use the verified feeler gage to verify the tubing micrometer. I paid less than $40 for mine, it passes QC in the inspection room at work, ymmv. After that start taking several measurements of several pieces of brass to find an idea of how much clean up you'll need - more on this later (you'll need the feeler gage to set the cutter on your neck turner, using the same feel from validating your micrometers. I personally use the Forster collet rig, but to each their own). Here's where I get off into my own OCD. I remove the spindle from the sizing die and take em all the way down (tool deflection is a real thing and a sizing mandrel is a lot more rigid than the threaded decapping rod). At this point if you're curious, re measure the case neck thickness, and you'll see they are a lot more consistent than before. If you take several neck measurements from several pieces, you now have an even better number to work from, and may even find yourself getting to keep some thickness you didn't have before (unless you have to turn to a specific OD for a custom chamber) just remember to keep about a thou and a half per side clearance (I believe this was mentioned before). Now with your brass sized (ensuring the shoulder is at the same location), and re-measured, trim them to the same length so that you don't have some necks turned into the shoulder some stopping at the junction, and some stopping short. Now that you have all this done, start turning, plan on losing the rest of the day... be sure to use some kind of cutting oil, heck WD40 works in a pinch. At this point, with my cases, sized, trimmed, and turned, I'll anneal them, and be done with it until I hit them with the mandrel one last time (this is done as part of the loading process since all the previous work was done on my Forster press everything going foreward is square and concentric with the case head) drop powder, seat the pill and then go shoot.

Now to address the costs. You can be all in for under $250 figuring $40 for the tubing micrometer, $20 for the feeler gages, around $100-$120 for the neck turning tool (depending what you get) then whatever mandrels and whatever holding die body you choose. Or... you may discover that after sizing and expanding on a mandrel that your necks are uniform enough, you can skip a whole mess of work, load some up, go to your favorite firing line and work on fundamentals and reading the wind... something I should have done before investing a mess of time and money into something that I couldn't reap the benefits of.

 

[epoletna]

I use a 21st Century neck thickness trimmer. It is like a small lathe that you can attach an electric drill to, and by running the drill (at low speed) you push the case slowly onto the mandrel and trim the thickness and the neck/shoulder angle (if needed) in one cut.

It is perhaps overkill for what you are doing, but I shoot two calibers for which there were no commercial cases when I first started bench rest shooting, and if you neck a case up or down you will have case neck thickness issues.

It also trues the neck, making it the same thickness all the way around.

For the 21st Century, you need to outside size the case neck, then run an expanding mandrel into it, before you start the turning process. This gives you a consistent inside diameter. You must also have the correct size turning mandrel to push the case into in the trimmer, and I find a little Imperial Sizing wax on the mandrel makes the turning process easier.

But remember, you are squeezing the neck down in a resizing die (without a resizing button), then expanding it on an expanding mandrel, before turning it. That way you get a consistent inside neck diameter, which should give you a consistent neck tension on the bullet after you have turned the outside diameter.

As someone has already pointed out, you only need to do this once on each case.

 

[theosmithjr]

I always run my brass through a turning mandrel before neck turning. Doing so will create a smoother fit on the neck turner and keep things cooled down.

I have the CORRECT SIZE MANDRELL for each Cartride I turn the necks on. You should ONLY NEED to TURN YOUR NECKS if you had a Gunsmith Chamber your rifle TIGHT as if used for, or as a BENCHREST ACCURACY Rifle. In that case you'd need CUSTOM DIES to neck size for your chamber. WHY ARE YOU THINKING of TURNING the NECKS? IF your rifles chamber requires this YOU'D OF NEEDED TO TURN THE NECKS 1ST BEFORE YOU EVER WOULD BE EVEN ABLE TO CHAMBER A ROUND? I DON'T UNDERSTAND YOUR REASONING HERE. You say you have HUNDREDS of rounds, you TURN NECKS FIRST! That's the ONLY WAY THEY'LL CHAMBER! AND YOU ONLY HAVE TO TURN THEM ONCE for the ENTIRE LIFE OF THE CASE! ?????????
Theosmithjr

You should be just knocking the high spots down to the least common denominator unless you have a neck-turn required chamber. In any event, I don't advise going under .010" thickness. Most of mine run .013-.014 neck wall thickness. The ball micrometer is an important part, get a good one. Doing this particular thing wrong is massively worse than not doing it at all.

How do you know they "need" trimmed? Needing case neck trimming is usually a function of having a deliberate tight neck chamber that won't accept brass of standard thickness. The normal distribution I see in neck thicknesses in any single bag of brass is ~ +/-.001 from the median.

 

[30BR]

[QUOTE="...That's the ONLY WAY THEY'LL CHAMBER! AND YOU ONLY HAVE TO TURN THEM ONCE for the ENTIRE LIFE OF THE CASE! ?????????
Theosmithjr[/QUOTE]
You can still turn the high spots off after being fired. This will help give the bullet a "cleaner" release. Just use a conventional sizing die without expander, so that the neck gets sized all the way to the shoulder. Then run it through the expander mandrel. (Bushings leave a section unsized.) Lots of across the course shooters do this with match chambers which are not tight neck. Is it worth it? Yes, if you don't mind spending the $$ and time.

 

[James D Crawford]

I am ASSUMING that this is for a std chamber; not a "tight neck" like many shoot in benchrest. All brass, even Lapua, will be uneven in thickness at the neck. You cut the necks to make that OD more uniform. Especially with a std chamber, you don't want to take too much off the neck wall thickness, because doing so means the remaining brass has to expand that much further to get a good seal upon firing. Excessive clearance will lead to premature neck cracking for that reason. So what you want to do is turn the neck just enough to take off the thickest spots.
FIRST, and VERY important, trim all the brass to exactly the same length. If you don't, your neck cutting tool is going to either cut too short, leaving some of the neck uncut near the shoulder, or it will cut some brass too far into the shoulder, weakening the case.
You next need to run the brass over an expander mandrel, to make sure it is round and opened up to PRECISELY the right ID for the cutting tool's mandrel. So you want to buy your expander mandrel and your cutter from the same company to make sure you have a perfect match.
Measure the existing brass wall thickness at 3 0r 4 spots on the neck. You want to cut that brass just so the high spots come off, not necessarily the entire circumference of the neck. (That could lead to excessive clearance.)
When you buy the tools from 21st Century, they may have many choices.
http://www.xxicsi.com/neck-turning-tool-kit.html
I like the titanium nitride because they can run without lube if you cut slowly and don't allow the tools to heat up.
You need to adjust the cutting depth so that only the high spots are taken off. Do this very slowly and measure the results. Adjust the DEPTH of cut so that the cutter just kisses the shoulder. (The reason you need the correct ANGLE on the cutter). Now lock everything down gently, and cut another piece and measure it to see if anything shifted.

Keep some ice wrapped in a towel handy so you can rest the cutting tool on it between cuts to keep it cool.

IF you had a tight neck, you would cut all the way around so that the loaded round would have about .0015" RADIAL clearance or .003" total clearance. (For example, a .262 6mm neck chamber needs the brass to be cut to about .008" thickness. .264 + .008 + .008 = .259").

Hope that helped.

By the way, many now go with "no turn " necks in benchrest because the task is so tedious, and you are better off spending your time learning how to read the wind.

And as far as inside neck reaming goes, every time I tried it, I ruined more brass than I fixed. My suggestion is don't do it. Leave THAT to the experts, who know how to remove the dreaded "donut". With a std chambering such as I described, you need not worry about a donut forming. http://www.6mmbr.com/neckturningbasics.html (note that article is about 14 years old I think...)

In a nutshell, my method & opinion exactly...but use the relatively sloppy fit of factory ammo when hunting dangerous game. Plus this most excellent 'tailoring-the-case' method only really applies to a specific rifle's chamber dimensioning...ammo made from such tuned cases should not be used in a different rifle, even if it chambers in a different rifle (for various reasons of safety and/or practicality). Tune specific cases dedicated to a specific rifle...also helps preserve most of your detailed work for repeated re-loading.

 

[bigedp51]

In the Redding bushing die FAQ it tells you if the case neck thickness varies more than .002 to use the expander that come with the bushing die.

And as stated in another posting above you only need to remove the high spots. And this means only turning 50% to 75% of the case neck. And also the thinner you make your case necks the further they have to expand.

I prefer using the Redding neck thickness gauge because with one turn of your wrist you see the amount of thickness variations. This helps if you use the gauge to sort your cases and not have to turn the necks. And with the average off the shelf factory rifle and standard dies with a expander the neck irregularities are pushed to the outside of the neck.

 

[30BR]

[QUOTE="... with the average off the shelf factory rifle and standard dies with a expander the neck irregularities are pushed to the outside of the neck." [/QUOTE]Which is a great reason to turn necks then throw the expander away. Once irregularities are pushed outside, then accuracy suffers because the projectile path into the throat varies depending on how that case is indexed inside the chamber. In other words, with the high spot at 11:00, it will shoot a little different when that case is indexed in the chamber at 7:00 or 5:00. (Love the Avatar!)

 

[ronstone09]

I've used the sinclair neck trimmer for years with good success as I have a very tight chamber in my target rifle and have to neck turn !

 

[birdiemc]

Dont know what happened to OP, but I'm loving this. Very good info coming. Thank you to all for the advice