Neck turning, to get accuracy?

J

JRB

Guest
Just after some tips in getting the necks turned to an accurate thickness. And what tolerance that might be?
I have noticed with some of my cases, that i am still getting neck seating variations,
What tips do you have to get your necks a uniform thickness and also getting a consistent seating tension?
Does neck wall thickness change after a number of firings?
With the excess you trim off, where does that originate from?
Jim
 
With the right tool, and ordinary care +- .0001 is the standard (for turned necks). I get better than that all the time. With the right equipment, it is pretty much automatic. If I feel variation in a set of cases for my PPC, I sort, and shoot like with like. I need all the neck tension that I can get with 133 and necks that are around .008 thick (for a .262 chamber neck), so annealing is not an option. For other situations, annealing is the common approach to more uniform seating force. Cases get longer from the brass in the body being force up into the neck. When you reduce a case's body diameter, and bump the shoulder that brass has to go somewhere. With one piece dies, that over size necks, and use an expander ball, there can be a stretch factor as well, but no one uses that kind of die for serious accuracy work, unless it is with a chamber that has been designed around the die, or the die has been modified so that its neck ID is not too small. With repeated firings and sizings, the neck can get thicker right next to the shoulder. This is commonly referred to as a doughnut. If the shanks of your bullets are seated into this area, it can cause a problem, and will need to be dealt with. If your bullets' shanks do not fall in this area, it is not a problem. (IMO)
 
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Boyd,

Why is annealing not an option for you? Is it the thin necks or the need for a lot of neck tension...or both?

Dennis
 
Thin necks mean that there is less seating force to begin with, and annealing would reduce that. If I were shooting a powder that did not "like" higher seating force, this might not matter. Perhaps LT23 would be this way. On the other hand, thinner necks reduced the absolute value of seating force variation. I shoot each batch of brass in rotation so that I can get a consistent shoulder bump, with a give die setting, and so that necks work harden at the same rate, or as close as then can. Beyond that, if I notice a bullet seats harder or easier, I set that round aside, and group it with others that are similar. The same is true of bolt close on a unloaded case. They can all be firm, or easy, just don't mix.
 
That's what I thought - thin necks and a lot of tension preclude the annealing process for your situation. I'm curious about your method of determining the seating force consistency. Do you just "feel" it (and how do you do that?) or do you use an indicating system like the K&M or the 21st Century? I'm using a simple arbor press and I can feel some differences, but not enough to really separate into more than 2 (easy - harder) sets.

Dennis
 
If you seat a few bullets with an arbor press, or even with my Harrell's Combo press, you get the hang of it pretty fast. Obviously one cannot put numbers on this way, but I think that meaningful distinctions can be made. The trick is to slow down and pay attention. I might adapt an indicator setup to my arbor press sometime. I have a Jones arbor press, and a stack of Belleville washers that are the same ones that are used for the K&M unit.
 
Many Thanks!

Boyd,
That has been very helpful!
So i was thinking that some variations in neck thickness was giving me a different seating feel, but rather different brass structure is what it really is.
I know my neck thickness is fairly even, since i changed over to a pumpkin and have been using a two stage process.
Do you find that once your cases are batched, for neck seating feel, so to speak, that they stay consistent, or they can vary each time they are loaded?

Now what is the best method to turn a consistent case neck thickness, i have been using TB advise from his book,
What variation is acceptable? i have been able to achieve less than .0005" at a guess, with most being around .0002".
Do i need to separate some cases out? Or if i read this again, is neck tension the 'factor' and neck thickness a 'means' to get some consistent tension?

Jim
 
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What are you measuring the thickness of your necks with ?
How much are you turning off your necks? What is their thickness after turning? With a turner like you are using, and a proper expander mandrel and die, I would expect to turn necks to no greater variation than +-.0001. If you are really seeing a variance of .0005 there is something wrong with how it is being done. Walk us through your procedure.
 
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