Tech Tip - Neck Tension vs. Time

[Mark Walker in TX]

Taken from the daily bulletin:

"TECH TIP–Neck Tension vs. Time

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I found this interesting, and am curious if there is more to the story. What I am wondering is do the necks continue to tighten and stiffen over time, even if loaded?

Seems another test might be in order. In this test you would, for one data set, size the case, seat the bullet, turn around and pull the bullet and measure that force required.

Then for the second data set, you would size the case, seat the bullet, then wait two weeks and pull the bullet while measuring the force required.

If more force is required 2 weeks later, then the brass is still behaving in the same manner.

Just a thought.

 

[Mark Walker in TX]

Any ideas on how to measure the force of pulling the bullet?

 

[BoydAllen]

No need to pull the bullets. Just seat them long,and then with one batch note the force needed to finish seating them to the desired OAL. Another batch can have the same thing,measure the force needed to finish seating to desired OAL) done two weeks later. Alternately, the second batch could be larger and divided into sub groups that would be done at various times to produce a graph of average force required over time.

Note- The following link will take you to an outstanding page on this subject. Be sure to look at the whole thing.
http://mywebpages.comcast.net/jesse99/tension.html

 

[Forum Boss]

Boyd has explained one technique. I should say, however, that the results might be different than what James Phillips observed because he was working only with sized necks. If you seat a bullet and then simply wait, that is going to hold the neck in a larger diameter,sort of like pre-stretching a holster by keeping a gun in it for a couple weeks).

One of the easiest methods to measure bullet seating force is to use the K&M arbor press shown in the original artical. It uses a vertical rod attached to a belleville washer stack,acting like a spring) to activate a dial indicator gauge. Resistance on the bullet in the neck compresses the washer stack and this is measured by the dial indicator. The more resistance, the higher the gauge reading.

 

[jb1000br]

This phenomenon probably depends whether one uses a bushing only, or has an expander ball in the die...

JB

 

[chris308]

I have noticed during neck turning that cases expanded right before neck turning cut differently than cases that were expanded and left to sit awhile.
I`ll try to do 10-15 cases at a time but sometimes 10-15 cases sit for a week or more after i expand them and am able to come back and start turning them again. The depth of the cut is noticably different between the two.
This is probably the same thing with neck sizing at different times,??) chris

 

[Lane]

All brass is not equal in hardness. All brass is not equal when subjected to heat in manufacturing or heat in your particular rifle chamber. Manipulation of the brass case from heat will not be the same from case to case. Expansion and contraction,spring-back)of the brass will be different as-well in different areas of the brass case. Your concentricity gage is accounting in part for this expansion and contraction,spring-back) with the external dimensions of the brass is specific areas of the brass case and the brass hardness. Personal point of view. Lane

 

[rlbell]

chris your correct brass will be a diffrent dia. if expanded then turned at a later time,that's why I expand about 10 cases,turn them then do another 10,necks are more consistant

 

[NeilNE]

Does Sinclair make a gauge for there arbor press that does this? If so what is the part number?

 

[BillK]

To whomever does this experiment. What are you going to use to prevent cold weld from skewing your results?

 

[Lane]

This is why some go to extremes with match prep brass by starting with a measurement of run-out of the case web,new Brass). The question is the uniformity of the brass in hardness and how it will flow and spring-back from the web of the case forward before you fire-form the batch and after subjected to the heat in the particular chamber. Match prep is never ending? All brass is not equal case to case. Lane

 

[dreever]

I feel that what matters most is consistently waiting the exact same amount of time between sizing of the neck and loading the brass. Dosen't matter if it's one hour or one week just make sure you have the same time lapse every time. If something comes up, and I can't re-load the sized brass on schedule I'll neck size it again and wait the prescribed amount of time before finishing up those rounds.
That's what I do, and it seems to work for me.

Danny