case neck tension tightening over time

[jb]

i have found that case neck tension tightens over time even if it's not loaded. the longer the time the tighter it gets. some big game loads 3-5 years old have the groups open 2-3 in" untill bullets are seated .005" deeper. has any one done bullet pull tests on different aged loads? would correctly annealed neck help this problem? my 25-06 made from 30-06 cases seem the worst. all my loads on all guns seem to open up on loads over time.

 

[Travelor]

I think what you are seeing is neck hardening rather than shrinking. Brass has a tendency to harden over time. Also, there is some evidence of brass/copper bonding that occurrs over time.

 

[jb]

also would the lee collet sizeing die make a difference as it causes the neck to spring out after sizing instead of spring in?

 

[Winchester69]

Some big game loads 3-5 years old have the groups open 2-3 in" untill bullets are seated .005" deeper.

This part sounds like galvanic bonding. Your breaking the bond with the additional seating is an appropriate remedy.
.

 

[dantiff2]

August 24, 2008
TECH TIP–Neck Tension vs. Time
Filed under: Reloading, Tech Tip — Editor @ 12 am
This may surprise you. We’ve learned that time,between neck-sizing operation and bullet seating) can have dramatic effects on neck tension. Controlling neck tension on your cases is a very, very important element of precision reloading. When neck tension is very uniform across all your brass, you’ll see dramatic improvements in ES and SD, and your groups will shrink. Typically you’ll also see fewer fliers. Right now, most reloaders attempt to control neck tension by using different sized neck bushings. This does, indeed, affect how firmly the neck grips your bullets. But time of loading is another key variable.

James Phillips discovered that time is a critical factor in neck tension. James loaded two sets of 22 Dasher brass. Each had been sized with the SAME bushing, however the first group was sized two weeks before loading, whereas the second group was neck-sized just the day before. James noticed immediately that the bullet seating effort was not the same for both sets of cases — not even close.

Using a K&M Arbor press equipped with the optional Bullet-Seating Force Gauge, James determined that over twice as much force was required to seat the bullets which had been neck-sized two weeks before. The dial read-out of seating force for the “older” cases was in the 60s, while the seating force for the recently-neck-sized cases was in the 20s.,These numbers correspond to pounds of force applied to the bullet). Conclusion? In the two weeks that had elapsed since neck-sizing, the necks continued to get tighter and stiffen.

Lesson learned: For match rounds, size ALL your cases at the same time. If you want to reduce neck tension, load immediately after sizing.

Comments

 

[overbore]

I have a different yet similar finding in that I load 7.62 once fired GI cases in batches of 500 by cleaning, lubing, resizing,, Dillon carbide) priming etc but in a recent finding, I allowed about 60 days to elapse between resizing and finishing the reloading process. In those 60 days the cases went from slip fit into case gage, each, to push fit and the necks expanded!!! Holy Cow, Batman! In 50 years of reloading I have never seen this. In the language of our new population, Que Pasa? all ideas greatly appreciated. Cordially, Overbore

 

[dantiff2]

If you live on the other side of the equator where water cyclones spin the other direction then,, TA DA ) !!!!!!

Dan

 

[overbore]

I know a nice quiet valley in Chile so if you pay the move, I will pay for the tests---otherwise back to head scratching. I am recycling all primed brass and trying do delay procedures---Overbore