Question about neck wall thickness and neck bushing size.

[EchoDeltaSierra]

I've been in the process of digging deeper into understand reloading and playing around with with several different things. That said, during my most recent reloading session with a FL neck die, I noticed some of the brass a bit loose in the neck. I do have a neck bushing that is another thousandth thinner, and this is the forth firing on this batch of brass and the were annealed prior to the first firing, and before the third.

My main question is, for those running neck sizing dies, do you find the need to reduce the size of the neck die as more firings on the brass occur?

Thanks, and please let me know if any of this needs clarification.

 

[remaction]

I assume you meant a full length bushing style die (there are full length dies, full length bushing style dies, neck dies and bushing style neck dies).
At any rate, I have not experienced neck walls getting thinner in my reloading past. Since you are annealing every other firing, that should eliminate hardened brass that could "spring back" and not hold to the smaller sized dimension. I have fired brass many times without annealing (before I got started in annealing) without experiencing that. All that being said, many times a thousandth tighter bushing seems to shoot better for me.

I am assuming you have not changed anything, and that you are using the same lot of brass as when you started?
I also assume you have not neck turned the brass, correct?
You may just have a few cases that have thinner neck wall thicknesses, have you checked them?
If one bullet seats tighter into a case, set it aside. If one seems to seat loose, set that one aside also. Then pull the bullets in those two and check the neck wall thicknesses on the 2 pieces of brass. If one case is a thousandth smaller than the other then you may want to go one bushing size smaller in order to get the thinner necks to hold the bullet in the manner you desire.

 

[spife7980]

I have heard of the necks getting thinner. Each firing they stretch outwards a bit and, like stretching dough, eventually it will tear when it gets too thin. When sized back down that stretching can’t be forced back into the brass below it without internal support. You just squeeze and fold it smaller again. If it wasn’t getting thinner, and since you can’t force it into the brass below it, it would buckle and crush in on itself as the path of least resistance when sizing it again. So since it gets stretched and pushed down that material that has been moved forward in the only direction possible. When you trim, that extra length is the lower brass diameter that misplaced and migrated forwards.

Neck sizing would see more of it I imagine since you don’t have as much as the case walls getting worked and pushed forward so the only movement would be in the neck.

I’ve never noticed it personally though as I always work the neck more than the bare minimum required and haven’t really bothered to measure them several firings in.

What was your original diameters and what are they now?
Are you running an expander ball?

 

[Huskydriver]

I have never seen that my brass has gotten thinner what I think may be your problem is that within the first 3 firings of the brass life, your brass springback rate is greater. If you were running bushing that is only .001" under your fired brass OD, it may not be enough to force the brass inward once the brass starts to harden under firing forces and resizing. I got a bushing for a 308 that worked great until my 3rd firing and then bullets would no longer seat consistently. Went down 2 thou and problem disappeared. I now anneal every other firing and don't have any issues running the original bushing. I also ran that lot of brass with the 2 thou under bushing and they survived well past 15 reloads without a large noticeable decrease in accuracy before my primer pockets gave out.

 

[remaction]

Huskydriver has a good point, I use more than 1 thou neck tension so that may be why I have not experienced this issue with the brass spring back causing problems.

 

[remaction]

I got to thinking about case neck thinning and went back to my notes from when I shot a 30x47 in Hunter Benchrest matches.
Ripley's Believe it or not:
I used Lapua cases and turned the necks to .0097 in order to provide .001 clearance between the loaded neck and the chamber (chamber at .330")
The loaded round measured .3279, so lets say .328" (the pressure ring on the Chism bullets was measured .3085")
I used a .327 neck bushing in the bump die, so .001" of neck sizing.
I fired those cases 70 times (give or take 2 firings), that's seven-zero, total over two seasons without ever annealing!
They were still shooting lights out, but man the brass in those necks had to be hard.
Not once did I have to go to a smaller bushing in order to get the bullets to stay seated.
However, benchrest chamber tolerances resulting in very little expansion of the neck and body.
Your mileage may vary...don't take this as gospel.
I threw those casings out last year when cleaning the loading area. I sure wish I still had them in order to measure a few necks.
Call me crazy, but don't call me late for dinner.