Case web thinning, how much is too much

C

CWPINST

Guest
I am wondering at what point do you throw away cases due to excessive thinning of the web area just ahead of the case head? .005 can easily be felt with a bent paper clip or the RCBS multi-tool. The area around this "depression" is typically around .035-.040. I have a 30-06 that will develop about .005 of thinning after about 3 firings, with neck sizing only. I guess, I am asking, how much thinning is too much?
 
My thought is to toss them and start over. What sort of loads are you shooting? I have only seen this with a rough chamber and light or cast bullet loads.
 
The load is actually pretty stout. MV is about 3050fps with a 150 NBT.
 
well, you are asking for "thoughts" and that's all this is.....

I've never kept brass that showed any sign of thinning. I've always managed to set up to avoid it or changed to another chambering. My idea, my guess, is that the problem originates with the shallow (17 degrees and change) shoulder.

Check to make SURE that your "neck-size-only" die isn't touching the shoulder.

al
 
If the chamber is oversized in diameter it can cause the problems you mention, but usually only with FL sized cases. As Al suggests, make sure that your NS die isn't pushing the shoulder back. Some factory chambers are disgracefully large while others are just normal SAAMI chambers. I've got three factory rifles that all seem to have good, for a factory rifle, chambers, and can FL size cases without too much fear of the case heads falling off early. I tend to load a little on the warm side as well.
 
Good info. The NS is a Lee Collet so neck pushback isn't an issue. The rifle is a factory Savage BVSS....factory barrel/chamber. The rifle shoots very well (around 0.5 MOA) as long as ES is tight, but strings vertical as ES increases. If I bump the powder charge up 1 grain the group shifts up 1.5 MOA. Likewise for decreases, and I mean plumb line vertical. I haven't totally figured that one out yet. Tried bedding, and different action screw torque. Re-crowning seemed to help some.
 
Last edited by a moderator:
Case web thinning, how much is too much?

CWPINST ........

You can actually measure the thinning of your cases above the web. The "old paperclip method" just isn't that accurate. The RCBS CaseMaster does a very good job of measuring this with far better accuracy.

Case thinning above the web should not happen when most calibers are properly resized. However, factory loaded belted magnums headspace on the belt, and the shoulder often has over .020" chamber clearance "at the shoulder". Because of this, it's common to notice some thinning "just above the belt" on the very first firing. It's important to headspace belted caliber handloads on the shoulder with less than -.002" maximum shoulder setback.

I measure the case thinning and toss any case that reads -.002" or more. Otherwise you'll have very short case life, especially when reloading belted magnum calibers. I have never experienced a headspace separation this way.
 
CWPINST, In your post above you mention going up 1 grain in powder. Did you go up 1 grain at once or did you go up 0.1grain at a time till you stopped at 1 whole grain?
Centerfire
 
Nope, 0.5gr. at a time. It equates to about 40-50fps per .5gr. That is what I worked up to......just stating the end result not the process. Going up 0.1gr in a 30-06 case is anal in the extreme. FYI, I used the Casemaster to measure. Practically every caliber I use (except for AI) will eventually get thinning even with collet NS only. What I wanted to know is how much is too much. The surrounding wall is about .035-.040. I have been throwing away when I get around .005 less than the surrounding wall thickness. In other words, if I start with .035, when It thins to .030, I throw it away. FYI, I never push the envelope to the point that I get loose pockets. Still can't figure out the vertical thing.
 
I'm in absolute agreement with German. And may I add to my earlier post, what I'm trying to say is that the shallow shoulder angle on the -06 allows the firing pin to drive the case forward and RESET THE HEADSPACE.

If your die is in fact not touching the shoulder then this is the only logical explanation in my mind.

al
 
exceptions, exceptions, exceptions ...

I also wrote an article on this subject. http://www.larrywillis.com/headspace.html
For non-belted handloads there is no acceptable inside case wear, because it's easy to control.

However, when reloading belted magnum calibers, this case thinning begins at the very first shot. I'm no fan of the "parperclip method" of measuring inside case wear. If you actualy "measure" the case (like I do), you'll do well to toss any case when it reaches - .002" Otherwise the case life of your belted magnums will be very short. I can't imagine how many belted cases I've reloaded, and I've never had a single problem.
 
You must log in or register to reply here.
Back
Top