Another kind of runout

[918v]

Ever seen a case bulged more on one side than the other? This is most noticeable after sizing. It bugged me to the point where I reversed the bases on my runout gauge and measured casehead runout of fired/sized cases. I found that the best cases had .002" TIR at the casehead, whereas the worst had as much as .006" TIR. Those were the cases where the body expanded completely on one side and none on the other.

So I'm thinking the .006" TIR cases are crap. But they also turn out to deliver the lowest runout at the bullet ogjive. I have one round with zero runout at the bullet and .006" at the casehead.

I dunno what to make of all this.

 

[Winchester 69]

Re: Another kind of runout

Do you have a ball mic? Sounds like uneven case thickness.

 

[918v]

Re: Another kind of runout

Yes.

It is either uneven case thickness or the case is softer on one side than the other. But why is the runout at the ogjive so low?

 

[nicholst55]

Re: Another kind of runout

I've heard of similar occurrences, but mostly on milsurp rifles with <span style="font-style: italic"><span style="font-weight: bold">very</span></span> sloppy chambers (can you say <span style="font-style: italic">Lee Enfield</span>, boys and girls?). I would sincerely <span style="font-style: italic">hope</span> that a 'precision rifle' would not have that sloppy of a chamber, but I suppose it is possible.

The way it was explained to me is that the case is laying on the bottom of the chamber, instead of being reasonably centered. When fired, the only directions for the case to expand, or obturate, is <span style="font-style: italic">away from</span> the direction where it's laying, hence the uneven expansion.

Not sure what the solution would be, short of either rebarreling, or setting the barrel back and rechambering.

 

[kombayotch]

Re: Another kind of runout

Bullet runouts are low because they're taken relative to the case body, not the case head. It makes little difference where the case head is. Your bolt face recess is not tight around the circumfrence of the casehead. Its loose. It isn't a two point alignment between the case neck and the case head. Bottle neck cases rely on a surface alignment between the case body and the wall of the chamber. What matters is that the necks are concentric relative to the body and that the case head is square relative to their axis.

If you have low bullet runouts with your formed cases, don't worry it.

 

[918v]

Re: Another kind of runout

It speaks to quality.

I just finished spinning Lapua, Hornady and BHA brass and found the following:

Lapua- 0-.002" TIR (funny that unfired cases were 0-.001")
Hornady- 0-.003" TIR (only 1 case was .003", the rest were under .002")
BHA- 0-.006" TIR (about half were under .003")

I think I'm gonna stick with Hornady from now on.