Neck Tension

[Poconolg]

I am using Redding bushing neck sizing dies. Generally do you get better accuracy with more or less neck tension?

 

[Hunter2678]

Most bench rest and long range shooters I know, including myself run .002 NT. I've also run .003 with good results as well. IMO .002 is a great place to start.

 

[F. Guffey]

I run bullet hold, I can measure bullet hold in pounds, I can also use interference fit as in the inside neck diameter and outside bullet diameter. The problem with interference fit is neck tension; there is no way to convert neck tension to bullet hold.

I do have tension gages, all of my tension gages are calibrated to pounds, I do not have a scale that converts tensions to pounds.

F. Guffey

 

[243winxb]

Bushing Die

2 thou is good. Siziing 1/2 of the neck makes a difference, after it expands to the rifles chamber, for me in 243 win.

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[F. Guffey]

I can also use interference fit as in the inside neck diameter and outside bullet diameter

But I have no way of converting interference fit to tensions. It always comes back to pounds of bullet hold. I can measure bullet hold when pulling a bullet and I can measure bullet hold when seating a bullet. Again, I have tension gages, all of my tension gages are calibrated to pounds, the first one I operated was calibrated in thousands of pounds, for safety sake the use had to use quick math. The user was required to multiply the reading on the gage by the number of cables.

And then there are deflection gages, same thing, no tension reading, most of my deflection gages were referred to as 'snap' gages. I believe they were called snap gages because the gage was snapped on.
F. Guffey

 

[Reloadron]

Mr. Guffy is making a very good point where he mentions An interference fit, also known as a press fit or friction fit. That is about what happens when we seat a bullet. There was a time when I would remove 500 degree F. parts from an oven and insert a part in them that was soaking in liquid nitrogen. Pretty interesting stuff.

Anyway here nor there and back to what Mr. Guffy is getting at. Using the term Neck Tension and expressing it in thousandths of an inch really doesn't say much. How much force I need applied to seat a bullet (compression) and how much force I need to draw a seated bullet out of a case (tension) tells me a lot more about what I have. This is a very good article on what we commonly call neck tension and all of the variables which effect it. Neck Tension — Not Just Bushing Size really gets well into it and makes what I see as some excellent points.

Bullet grip is affected by many things, such as:
1. Neck-wall thickness.
2. Amount of bearing surface (shank) in the neck.
3. Surface condition inside of neck (residual carbon can act as a lubricant; ultrasonic cleaning makes necks “grabby”).
4. Length of neck (e.g. 6BR neck vs. 6BRX).
5. Whether or not the bullets have an anti-friction coating.
6. The springiness of the brass (which is related to degree of work-hardening; number of firings etc.)
7. The bullet jacket material.
8. The outside diameter of the bullet and whether it has a pressure ridge.
9. The time duration between bullet seating and actual firing (necks can stiffen with time).
10. How often the brass is annealed
— and there are others…

What I care about most is uniformity. If I use a collet die to pull a seated bullet and record the force plotted against the travel I will see a breakaway force (the required force to get the bullet to break loose) and the needed force to continue to drag that bullet out of the case. Do I really care about those numbers? No, not really but what I do care about is plotting the same graph bullet to bullet to bullet. I want all of my loads to require the same force. As a US measurement I would express the units as lbf (pound force).

While expressing neck tension in thousandths of an inch is convenient it really doesn't tell the whole story.

Ron

 

[cw308]

Most of the info I've read .002 neck tension is where you want to be . Without being a rocket scientist the formula is measure the case neck thickness at two points on the neck. Example, case neck measures .015 x 2= 30 , bullet .308 total = .338 you would use the neck bushing .336 to get you the .002 neck tension. As per instructions , not me. Keep it simple & test.

 

[old roper]

This is from Redding.

http://www.redding-reloading.com/tech-line-a-tips-faqs/140-bushing-selection

 

[tobnpr]

^^^^.

 

[243winxb]

Find the smallest neck diameter of the lot .

If a loaded rounds neck diameter is X , the bushing needs to be .002" smaller. Don't matter if the necks are turned or not. Brass changes with or without the expander, but more with. Make sure the stamped numbers on the Redding bushing is facing down , towards the case neck.