Neck Thickness and Neck Uniformity

[Shynloco]

Folks,
I've not been reloading nearly as long as some of you and I've seen some very informative and knowledegable people express their opinions and experiences on this blog in an attempt to help others who seek ultimate accuracy from the rifles they reload for. And occasionally, I read conflicts between what I consider "expert opinions" from those who both practice what they preach and can back it up on the range in the scores they shoot. And in my pursuit of chasing that five shot one holer, I've read articles, comments and books by some of the premere Benchrest Competitors in their practice of "precision reloading." I think we can all agree, that there are certain casing preparation practices that are necessary in order to achieve what is call uniformity or "consistency" in every piece of brass we prep during reloading. By that I mean weighing, sorting and some believe in turning necks and annealing, while others (not necessarily competitors) chose not to turn necks and do not anneal. My guess is folks in either camp have tested their theory which leads them to why they do or don't do certain things. So bare with me because I found something (of concern) in my pursuit of perfection for preparing each piece of brass the same in order to attain uniform neck tension, something that most believe is critical to ultimate accuracy.

Not long ago, I started prepping new Lapua brass for my recent 6.5 X 55 rifle conversion. An issue arose where some brass did not meet the concentricity variance standard so I purchased a second group of brass, presumably being a different lot of Lapua brass (I didn't buy full boxes, hence the difference in lots). I did all the usual detailed preparation and then fireformed the brass. I separated the brass into groups where they weighed within 1 gr of one another. I then turned the necks on one group, but didn't turn the necks on the other. I loaded both these gropups with the same bullets, same depth seating and same powder loads. I then shot these groups and reloaded them twice more using the same criteria while developing the powder loads to find the best number of grs my baby liked the best for that bullet. After being able to get the five shot groups (100 yds) down to around the size of a quart, I took note of whether it made any difference in terms of accuracy, whether it matters that necks are turned or not, for my particular rifle. What was started buggin me some, was that though everything "seemed" to be identical case wise, I could "feel" a difference in neck tension when seating the bullet using my Wilson In-Line die which is how I seat my bullets in all the calibers I reload for. So what I found, was that turning all the necks made the neck tension uniform (except for a few casings that I'll anneal to see if they can be rehabilitated). But thats when I tripped across my "issue" that perplexes me some. And that occurred while I happened to be measuring the neck thickness of my groups AFTER having used the same Neck Turning tool with the identical same setting on all the piece of brass. What I found that there was a variance of .0004 - .0007 in neck thickness even after that Lapua brass had been turned with the identical same setting and tool and had been shot the same number of times.

SO why do I have that much of a variance in neck thickness, don't necessarily feel any significant difference in neck tension AND does that neck thickness variance mean anything in terms of accuracy? I invite any and all comments and opinions on this issue as I've become completely anal in my pursuit of perfection in my reloading. Thx to all for reading such a lengthy post.

Alex

 

[BoydAllen]

Two things:
What tools did you turn and measure with?
I hope that you meant .0004 to .0007 and not four to seven thousandths, as you wrote.

 

[Shynloco]

Evening Boyd,
You are definitely one I'd hoped would respond. And my bad...senility setting in with the numbers. I use an NT1000 Sinclair Neck Turning Tool with Sinclair Mandrels; Mitotoyo Ball Mic and a Starrett Caliper for my measurements. Thx!

 

[BoydAllen]

Before you turned the necks, you should have run the cases through a one piece FL die (with lube) set so the die sized all the way to the shoulder, and then expanded the necks with a expander mandrel sized to produce the proper fit on the turning mandrel, which should have been made of carbide. If there was room in the neck part of the chamber, I would prefer to have fired the cases one time, with a good stout load, before sizing, expanding and turning. When turning with power, let the cordless tool move as the crookedness of the case dictates, and let the turning tool do the same. Use the slowest speed, and keep things well lubricated. Go to the shoulder fast, making a rough, incomplete cut, intentionally leaving a lot of unturned brass behind, and then come off very slowly, creating your finished cut. Don't go back onto the neck with the cutter after that. Trying to hold things rigid will increase runout. If you follow these directions, your necks should be well within +- .0001. Let me know how this works for you.
Boyd

 

[Shynloco]

Boyd,
Thx for the suggestions. As you may be already guessed, this has been a learning process from the git go as I only first started this "precision loading" effort about 1.5 years ago and reloading my own loads 3 years ago. It has been much of a learning curve, but I've become the proverbial junk yard dog who only craves more in search of that ultimate accuracy.

And as for those casings, I actually had an issue from the git go as I put them through a FL die before fireforming them. I came up with around 16 out of 50 casings with bent necks, as determining by a concentricty variance of between .0005 - .0008 out, per my Sinclair Concentricity Guage. The FL was done with a Redding FL Die and the die was sent back to Redding who checked and verified it was within their standards, but determine all the pieces of new Lapua brass I'd sent back with the die were bad. Those were round filed and I started again. I also subsequently removed the expander ball and haven't used it since, but have the die which is working fine now. So the brass was put through the Sinclair Mandrel die, but when I turned them, I did it by hand, not using a drill. I actually thought it would be done more accurately than if I did it on my drill. So much for over analysing things. But I do have a new box of Lapua 6.5 brass on it's way and I will do as you suggest with a fast rough cut and then slow one on the return pass using a drill. I will also measure each casing and neck wall thickness before and group them if necessarily before the cut. I am really trying like heck to remove any and all variables I can humanly and possibly do. And I believe I have good equipment to do it. But as one of the other notibly bright people on this blog put it (and paraphrasing his saying), at some point I've become the weakest link in this effort.

But thanks for the input and I'll keep you posted on my progress.

Alex

 

[jlow]

It’s a good question as to why the neck thickness still varies by 0.0004 to 0.0007 thousands - I have wondered about this myself.

A couple of things, one is that I have found that I have to neck turn brass again after one firing for it not to turn anymore.

Second is what is the difference in the diameter of the expander mandrel and the mandrel you use for turning? They pretty much have to be different or you cannot get the brass in due to spring back – is that difference causing the slop you see? How much difference should you see.

I am not really posting answers but just the same questions based on what I have seen and so also curious to see answers.

 

[BoydAllen]

When I wrote to go to the shoulder fast, I did not mean that the rpms should be higher, but that the rate of travel along the neck should be faster than what would produce a smooth finish, and make sure that you FL size before expanding to turn. There is nothing wrong with using hand power to turn. My friend Del Bishop did all of his necks that way, and I would hope to become as good a shooter as he was in his prime. With power, I would try to hold the rpms to 120 max.

 

[memilanuk]

A couple things that can allow some errors to creep in...

Keep an eye on brass build-up on the expander mandrel. I don't know about other brands, but K&M mandrels seem to have a noticeable transition from the taper to the main diameter, and I do get a little brass 'ring' start to build up on there. Granted, I generally am doing fairly large batches (several hundred at a minimum). Some brands of brass (Winchester) are rougher internally and around the case mouth at this stage of brass prep, and leave markedly more of a ring behind. I've had to chase it off via a combination of strong ammonia cleaning chemicals and polishing. Definitely less of a problem with Lapua cases.

The other thing that can cause some noticeable changes in final dimension is turning too much, too fast, with not enough lube. Basically - anything that causes heat build-up in on the mandrel or in the frame that holds the cutter. A periodic drop of turning lube (available from Sinclair Int'l) on the mandrel helps reduce the friction factor, and keeping a bag of ice in a bowl close at hand and setting the turner body on that when you set it down to change cases is usually enough to keep every thing nice and cool.

YMMV,

Monte

 

[BoydAllen]

Because customers want and expect it, I believe that expander mandrels are manufactured so as to produce too tight of a fit on the turning mandrels that they are designed to work with. This is the source of all of the commonly reported turning heat issues. If you let the tool and the case float, and use proper technique so that the cutter is cutting the whole time it is on the neck, such a tight fit is not necessary. For my 6 PPC cases, I get around this problem by using an old Sinclair turner that has a mandrel that is smaller in diameter to make a rough cut. The fit is so loose that there is not heat or brassing of the mandrel (with lubrication). By taking all but the last thousandth or so off first, the necks' tightness on the carbide mandrel of my K&M tool is considerably reduced. That, and the fact that the carbide mandrel is much less prone to brassing keeps me out of trouble, and keeps my tool much cooler. A couple of other things that I have learned from experience are that a neck that has been expanded will shrink slightly over time, and the length of time that the neck is on the mandrel has an effect on its ID. Once, after my cordless screwdriver's battery ran down, I stopped turning for the day, having expanded all the cases, and when I resumed the task a couple of days later, I had to run the cases back over the expander again because they had become too tight.

 

[GermanS1]

Boyd, I have found the same thing with respect to time on the mandrel and time since expanding. I normally run the case into the expander twice, fairly quickly, then turn it right away. If I have to stop for a while (dinner, work, etc.) when I come back, I simply resume the expand/expand/turn cycle on the next case.

Alex - you're using Lapua brass, that's fairly thick stuff normally. If you're turning it down in one pass to a much thinner level, you might be putting quite a load on the cutter and that can be a source of some of your inconsistency. I prefer to keep each cut to no more tha 0.0015" and the final cut to less than 0.001". That won't eliminate variance, but it helps to reduce it.

 

[bozo699]

Alex,
Another thing that can appear to be inconsistent when measuring neck thickness is if your measuring the necks at the same depth every time you measure them, I think it was Mikecr that posted a picture of his Mitotoyo Ball Mic, he had a stop made on the mic so each piece of brass was measured in the same place each time and as you rotate the brass it is measured in the same place as far as up and down on the neck, if it isn't in the exact same place each time the brass gets cocked a little differently and consequently measurements vary, I have the same type of stop on mine and it definitely helps (FWIW)
Wayne.

 

[BoydAllen]

One thing that can mess up these measurements in a hurry is if you take them after trimming and the deburring operation leaves a small ridge on the outside of the neck and the end. I use a little 0000 steel wool to make sure that this is removed.

 

[memilanuk]

Boyd,

Just a minor point of clarification... when I mentioned the accumulation of a brass 'ring' on the mandrel - what I believe you call 'brassing' - I was talking about the *expander* mandrel, not the mandrel or pilot on the turner itself. While I don't doubt your experiences regarding the fit of the case on the pilot causing heat and/or 'brassing', that wasn't quite what I was talking about.

Monte

 

[GermanS1]

Wayne's point about measuring in the same place is an excellent one. On my tubing micrometer, I taped a little pad of leather to rest the case. It's been in place for years and thousands of measurements without moving.

 

[BoydAllen]

Monte,
I understood what you wrote, an was not referring to that detail, but referring to a common problem that can happen, especially with non carbide turning mandrels, with a tight fit, too many RPMs, and inadequate lubrication. When the brass transfers to the turning mandrel, it will generally happen at the point of highest pressure, right under the tip of the cutter, and this causes the necks to be cut thinner than desired.

Boyd

 

[Shynloco]

Gentlemen,
I truly appreciate all the responses thus far and know this is coming from some of the best reloaders and most knowledgable folks on this or any blog. I find it important to heade what you say because you can backup your recommendations on that target. I am truly thankful for the help.

UPDATE; Today I took the ten most radical and varied casings down to a good friend's home about 50 miles from me. He's an old time Benchrest shooter who is almost 75 years old, but no longer competes, but has more than 50 years experience reloading. Imagine the sight, a 75 year old teaching a 65 year old how to anneal. When I explained what I'd discovered in the neck measurement differences, he just laughed and said it's all about getting your brass to spring back the same. Annealing will cure that and you'll see that variance drop significantly. If a few still won't cooperate after annealing, throw them in the trash and go get some new brass. So under his watchful eye, your's truly annealed for the first time in his life. After the cases dried, I went home and took to the reloading bench. Went through all my detailed regiment in case preparation and then before loading the powder and seating the bullets, I remeasured all the case necks in the same spot. Guess what.... that variance that was there before was now no more than a .0001 - .0002 variance between all the cases annealed. And I loaded the powder and seated the bullets and what a sweet, uniform feel using that Wilson inline Seater Die. Made this amateur happy as a lark. Now the only thing left is to go shoot what I've loaded provided the crazy winds as of late, stop blowing up here in the High Desert.

Lastly, the downside of everything all of you and others have taught me this past year (mostly through your detailed posts on several issues involved in precision reloading) , is that I'm running out of excuses for not getting that five shot one holer. Perhaps a better rifle might also aid in my quest, but frankly I just don't have the funds for a very nice custom built Benchrest rifle. But thats ok...I've learned to make due with what I have and even though I don't have unreasonable expectations from my rifles, I still try my darnest to shoot the tightest groups possible with me behind the trigger. The word, "can't" isn't in my vocabulary and thanks to all of you, you keep providing more challenges and ways to better perfect what I'm doing.

My best to all you good folks and thanks for your continued help.
Alex

 

[jlow]

For my 6 PPC cases, I get around this problem by using an old Sinclair turner that has a mandrel that is smaller in diameter to make a rough cut. The fit is so loose that there is not heat or brassing of the mandrel (with lubrication). By taking all but the last thousandth or so off first, the necks' tightness on the carbide mandrel of my K&M tool is considerably reduced.

I am new to this so just trying to learn. The question is would not using a mandrel with a smaller diameter to avoid the heat issue potentially can cause an over cut on the neck? Assuming there is always some slop in the fit of the neck on the mandrel, what normally governs the degree of cut if one accidentally push the neck towards the cutter is the diameter of the mandrel and if the mandrel is thinner, would this not allow a deeper cut.

 

[BoydAllen]

I hold the cordless drill that turns the case loosely, as well as the turning tool. When I say loose fit (for the rough cut)on the mandrel, it is relative to a wring on fit. I slides on, but does not rock. Also, by always having the cutter cutting, it keeps the neck pinned to the mandrel. This is the key. As I have written before, I travel down the neck rather rapidly, intentionally making an ugly cut, and when I get to my stopping point, reverse direction and come off the neck very slowly. leaving a good looking finish. If I want to pay real close attention to what I am doing, I can make my rough cut as uniform as a finish cut. I have turned necks for a lot of years, and I have a Holland neck micrometer that measures to .0001. It just takes me a few seconds to check each case as I am turning them, and I generally do. All of my cases are closer than +-.0001. If you want to learn about turning, assemble a good set of tools, both cutting and measuring, clean up, size and expand some tossed brass from the range, and practice. You can make all of your mistakes on free brass. I use some of my supply to verify setup. Why risk mistakes on expensive brass?

 

[jlow]

Thanks for your response. Still not quite sure why one would not cause a problem using a mandel of a smaller diameter. Perhaps there is some misunderstanding on my part.

To show what I mean, here is an illustration that shows two possible situations when the mandrel is undersized. What you are seeing here are two cross sections of the neck area with the mandel (in grey) being in the middle, and the neck (in yellow), and the cutter on the side. In either situation, the relative location of the mandrel and cutter remains unchanged (as it should be) and the neck is allowed to float since the mandrel is undersized.

As you can see, on the left situation, the neck is pushed against the mandrel towards the right and the cutter is just kissing the neck with no cut. However, if the neck is pushed against the mandrel towards the left, the cutter can take a significant cut into the neck. What I summarize by this is that as long as the neck is floating, the cut on it will be inconsistent to the degree of the undersized mandrel.

 

[BoydAllen]

Because of the looseness with which I hold the cordless drill and the tool, there is virtually nothing pushing the wrong way, and pushing the neck off of the mandrel and into the cutter takes some force toward misalignment. To me is sounds like you are trying to bench race this. Go turn and measure some necks. That is the best way. I have and can do what I have described. If you are asking if someone who lacks skill, experience, or is intentionally trying to have a problem can have a problem, the answer is yes. I am just reporting what I do, that has been accurately measured. Often, what we imagine or expect is not what actually happens. If engineers could visualize everything perfectly, there would be no need for test pilots. There are several approaches to turning necks. Choose the one that suits you. For me, the method that I have chosen is simple, direct, and produces excellent results. I should add that I generally have found that for manual tasks, that the written word loses something in the journey from the mind of the writer to the hands of the reader, and that I really prefer to teach these things in person for that reason. Perhaps it is my lack of communication skills. In any case, good luck with your neck turning.
Boyd