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Neck mandrel sizing

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Modern thinking seems to be to use a Wilson neck mandrel as the last case prep process before priming, adding powder and seating the bullet.

I have a Wilson sizer and mandrel ( 338 and 308). However I wonder if it is really a good process to do? Limited testing that I have done has not been conclusive. I can and will do more testing but wondered what other people’s thoughts were.

 I use Redding comp bushing dies in a CoAx press - the dies are somewhat free floating so in theory self align. It occurs to me that although a mandrel die does the same thing unless the mandrel itself is perfectly vertical within the die any alignment error would be introduced into the case neck.. Also it is said that the mandrel makes the inside of the neck more concentric. Does this not happen when seating a bullet anyway? If the mandrel simply lowers neck tension or reduces neck tension variations due to lower neck tension I don’t see the point - I can achieve that with a larger bushing.

Thoughts  and experiences appreciated.

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I use one of these, and have several sets of pin gauges to set the neck tension.

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This is a photo of a mandrel die for controlling neck tension during preparation of match-level brass. This idea is that you can get very small, as well as consistent incremental changes in the diameter of the brass at the neck, therefore controlling neck tension.
The die body with nut is not caliber specific. It can be used on cases as short as the 6BR through the Remington Ultra Mag. With careful setup it can even be used for the .338 lapua case. It uses precision collets that are commonly used to hold milling cutters and drills in the machining industry.
You generally you need 1 collet per caliber but some sizes will work for multiple calibers. The common collet size ranges are;
6mm - .197" to .236"
7mm - .236" to .276"
8mm - .276" to .315
Mandrel pins are made from 2 " long precision hardened steel pin gauges. One end of the pin is tapered and polished. They are available in .0005" increments, and can be had in either "PLUS" (+.0002"/-0) or "MINUS" (-.0002"/+0) tolerance. 
 

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The collet system is much  better. The Wilson die I have uses a grub screw to clamp the mandrel in and it concerns me what the tolerances are.

The mandrels I have are basic neck turning mandels  marked T and E. for turning and expanding. In this case .33 cal for 338 lm. The tension with the T mandrel is ok - slightly reduced from using no mandrel but unable to measure any difference in neck diameter with decent callipers. Obviously a tubing micrometer is needed. 
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While I like the idea of neck uniformity, I question whether any kind of mandrel can do the job as described above. Setting neck tension by micro increments means that the brass is exceptionally uniform in dimension and metallurgy to begin with, and that your bullet diameters  are within a tolerance level that won't defeat your efforts. With care and sorting it is possible, but like most reloading endeavors, if you are not sorting out the components for uniformity, then the efforts are buried. Much like weighing powder to an exactitude, Unless you are assuring the case volume is identical, neck tension is identical, and bullet diameter and weights are identical,  weighing to an extreme is a probably a wasted practice. Just random thinking out loud here....~Andrew.

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1 hour ago, Andrew said:

While I like the idea of neck uniformity, I question whether any kind of mandrel can do the job as described above. Setting neck tension by micro increments means that the brass is exceptionally uniform in dimension and metallurgy to begin with, and that your bullet diameters  are within a tolerance level that won't defeat your efforts. With care and sorting it is possible, but like most reloading endeavors, if you are not sorting out the components for uniformity, then the efforts are buried. Much like weighing powder to an exactitude, Unless you are assuring the case volume is identical, neck tension is identical, and bullet diameter and weights are identical,  weighing to an extreme is a probably a wasted practice. Just random thinking out loud here....~Andrew.

I agree with you regarding metallurgy, even annealed cases of the same batch can have slight tension differences in my experience.  I use a Redding mandrel and I do get modest improvements in performance over leaving it to the bushing to size.

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Andrew,

I think that you are right in that we ( shooters) tend to infer much from what we can actually measure. For example I’ve measured the H20 capacity of the odd case but to measure capacity of say 500 cases you tend to weight them and infer capacity- +/- 1 grain seems the norm but where did that come from and also when you trim the necks you change the weight without changing usable capacity. Also how do you measure neck tension - We can measure seating pressure but from advice on here you need a constant force source to get reliable readings. AMP have developed such a machine ( their video shows the relationship between annealing and seating pressure ).

Annealing, I think most competitive  shooters now do it but didn’t  Brian Litz say that there was no evidence for it showing accuracy improvements. 

I think that it comes down to where you set your own goals - for me I want consistent single digit ES over a Labradar. If I don’t at 1km I have at least a 6” vertical dispersion before any other factors. I am not there yet, often but not 100%. I try to make things more consistent in my reloading process. In the end the barrel determines the accuracy potential all I can do is make the reloading as consistent as possible - somethings like neck mandrels are cheap enough to try but the  Autotrickler took more thought.

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Ah! I have quit competitive shooting. The most I do is shoot across canyons at 1MOA targets dotted along the landscape out to 1860 yards. In this kind of shooting, the best and most conscientiously assembled handloads will be taken off course by shifting prairie winds -often blowing onto the target from two directions simultaneously. My rifles are accurate and my handloads are good but on somedays the wind gods just have their way with them. ~Andrew 

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11 hours ago, ds1 said:

Annealing, I think most competitive  shooters now do it but didn’t  Brian Litz say that there was no evidence for it showing accuracy improvements. 

There is empirical evidence to suggest thats not quite true these days.

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John, I don’t think that it was quite true when it was written. I vaguely remember  some of the articles in PS magazine about the likes of P.O. Ackley annealing brass by seating cases in a tray of water - gas torching the necks and pushing the cases over in the water. Thankfully a little easier these days. Even he Houston warehouse test eluded to case neck preparation as being one of the most critical aspects in the reloading process.

Andrew, certainly agree wind can affect vertical dispersion as well as horizontal but what annoys me is when I am making what I think are good shots and I get more vertical than horizontal spread. Eg last month at 1km I was using Lapua factory 250 grain lockbase ammunition ( not the best thing to use) but I wanted the brass to reload.  Wind was fairly constant and I had about a 10cm horizontal spead but 40cm vertical spread - the shots were like a line up and down the target. It would have been quite depressing on a one moa circular gong. I would probably have started chasing the error making it even worse - one shot high, next shot low routine.

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