The ultimate solution to neck tension
- Thread starter Joe R
- Start date
Joe R
Gold $$ Contributor
Trial and error. For my 260AI the .263 mandrel brought the seating pressure (as measured by the Hydro press) down from over 100 psi to ~60 psi. My guess is that a .2635 would bring it down to ~20 and a .2638 to less than 10 psi. Of course this is with my Lapua Palma brass with necks at ~10Ks. YMMV.
Joe
Not really. I collect my competition brass on a clean towel so I feel comfortable lubing and resizing it without cleaning it. I decap, body size, neck size, and then run a mandrel down the neck on a progressive press; i.e. these events happen in one handling cycle. The neck size die is selected based on neck thickness and is chosen to make the neck I.D. very slightly smaller than the mandrel.
Then I measure and examine the brass and trim/chamfer if necessary. Then I clean the brass using the wet SS tumbling method. Next I anneal (every time) and sort the cases after which they're ready to prime at which point I run the mandrel down the neck again. The brass is already at the desired size (or perhaps a tiny bit smaller due to spring back of the once fired brass), but in the event the neck is damaged or put out-of-round during the sizing, cleaning, or annealing steps, this second mandrel treatment will take care of any problems and since it's done on freshly annealed brass, it (in theory) produces a consistent and uniform neck ID. The size of the mandrel can be selected to produce more or less neck tension, as desired. I have several of them.
My routine lets me set the neck ID using a mandrel immediately after annealing when the brass has the least spring back. My sizing steps occur with brass slightly work hardened from one firing, but the body sizing and shoulder bumping is not ultra critical and the neck sizing is not critical because the final ID is set later on after annealing.
This gives me a chance at consistent neck tension without a lot of individual handling of brass.
I would think the neck tension is a contribution of the entire neck. It wouldn’t matter whether a small irregularity is on the inside or outside. Tiny irregularities would be a minor contribution to the total grip on the bullet. If tension is just a way to change burn rate, then only the total grip would matter. The big variable is variation in work hardening from shooting, sizing and annealing. What you may be accomplishing is more uniformity of grip around the bullet diameter if that’s possible? I don’t worry about details like this unless I see a difference on the target. I cannot shoot good enough to sort out tiny changes in my case prep. To see small improvements I believe you need to consistently shoot groups at 100 yards no bigger than a 1/4". If you make a 5% improvement you will never see it on the target. It gets lost among the other many variables. If a bullet isn't started perfectly straight into the neck is the neck shape altered? I seem to notice a difference in seating force between a flat base bullet and a boat tail, they both have a radius on the back? I assume my Wilson straight line seater doesn't keep the bullet perfectly aligned and it's being forced at a slight angle into the neck? I shoot a 6BR varmint rifle.
Joe R
Gold $$ Contributor
Hi Dennis,
Mine was a prototype so he had to do drawings and more to get it done so it wasn't cheap, but it was worth it to me. If you would like to ask him you can email him at kennethp@portersprecisionproducts.com
Joe
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Brians356
Gold $$ Contributor
"Old age - it's the only disease you don't look forward to being cured of."
"Mr Bernstein" in "Citizen Kane"
Joe,
Why do you need the segmented collet? I assume the mandrel is expanding the neck, unlike in a Lee collet die. How does the collet contribute here?
Joe R
Gold $$ Contributor
Try again, mine went through. Check your PM more info there.
The collect shown gives a far greater range of mandrels that a Lee collet die can. The one shown has a range of .236-.275 and that covers me for my 260 AI, the one for a .308 has a range .275-.314, about 40Ks. For my Lake City brass I had to use a .3087 mandrel to expand the neck and because it is so hard and has so much snap back and I could still seat the bullet with ~20 pounds of seating pressure. So it is good to have a wide range.
Joe
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Brians356
Gold $$ Contributor
I'm not convinced all the thick spots stay on the outside. Thicker walls will spring back a bit more, so after the neck relaxes, probably the ID is not as uniform and round as when it was on the expander mandrel. And the turning mandrel is not tight enough to force the variance to the outside while turning.
Also, a donut which is at, or adjacent to, the neck/shoulder junction will be even more difficult to force to the outside, since the shoulder acts like a buttress - when you push on the donut from the inside, you must also push against the shoulder, and there is a vector of that force is trying to compress the shoulder along its length, so the neck will spring back near the junction even more doggedly.
I've never proven any of this, but I have a hunch some of the laws of physics are still valid.
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Joe R
Gold $$ Contributor
A quick and easy solution is to take the beveled pin gauge and clamp it tightly in a collet puller (I have a Hornady) in the press....and presto (pun intended) you have a neck expansion die. The case float in the holder will allow for self centering. KISS principle.
I am sponsored by Holiday Inn Express.
I had tried this option in the past, but I couldn't consistently get the mandrel perfectly straight so I ended up with some crooked and some ruined necks. Originally a Hornady collet and a Lee universal decapping die were what I wanted to use as models, but when Kenny showed me this collet I knew right there it was far superior to those.
Kindest regards,
Joe
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Brians356
Gold $$ Contributor
What I was getting at was: How does the collet affect the neck? When you force the neck over the mandrel, does the outside of the neck also force the collet petals to open? And what's the benefit from that?
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I am using a 21st die and had the steel tapered mandrel Melonited. Lost track on how many Ks of brass has gone through it and still going strong, no wear whatsoever. No lube required, the die is in position 1 of the Dillon 650 set up for loading only. It cost me a buck to have the mandrel Melonited.
Skunce
Gold $$ Contributor
As I understand it the collet is only used to hold the expander pin in perfect alignment with the die and to hold pins of different diameters within the range of the individual collet.
Joe R
Gold $$ Contributor
Exactly.
USMCDOC
Silver $$ Contributor
No, it is a "ER" type collet, once it is tightened.. it ain't going anywhere!
Drat, Foiled again Batman....
Too good to be true for that to work eh Joe? I never tried it as I use a K&M expander for the times I shoot .001" NT. I could see where it would not be precise enough to hold a dead true on the pin in relation to the neck long axis.
Joe R
Gold $$ Contributor
Brians356
Gold $$ Contributor
I see. In the photo it's not clear that the collet is tightened on the mandrel. So the mandrel is coaxial with the die. What assures that the case is also coaxial?
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