OzFclass

Hi All
I noticed this recently



I can’t tell you how many firings the case has had.

There are a few other cases with a mark showing around the same distance down the case.

Time for some new brass??

Cases have the shoulder bumped approximately 2 thou each time.

Just wondering what caused it?

Case head separation. Brass worked too many times causes the case wall to thin out.

Read this article:
https://www.accurateshooter.com/technic ... diagnosis/

And then go and make one of the paper clip thingys and check your cases.
Pete

Too many firings, Too much pressure, Oversizing case, Sizing Die is under size to chamber, leaving lube on case, not cleaning out chamber after cleaning,Over Annealing (IMO).

If the case does not grip the chamber wall it will grow and separate like you have .

BRETT B wrote:Too many firings, Too much pressure, Oversizing case, Sizing Die is under size to chamber, leaving lube on case, not cleaning out chamber after cleaning,Over Annealing (IMO).

If the case does not grip the chamber wall it will grow and separate like you have .

Thanks for sharing all my reloading techniques...

So I may have done something wrong??

hi...most likely cases are worn out ....being a saum a lot of pressure...just chuck em all nd get new cases...

Tim N wrote:

BRETT B wrote:Too many firings, Too much pressure, Oversizing case, Sizing Die is under size to chamber, leaving lube on case, not cleaning out chamber after cleaning,Over Annealing (IMO).

If the case does not grip the chamber wall it will grow and separate like you have .

Thanks for sharing all my reloading techniques...

So I may have done something wrong??

Tim,

Oversizing the case is the usual suspect for case separation. Do you measure base to shoulder before and after bumping? If oversizing is the culprit, you'd expect it to be accompanied by a lot of case length trimming? (the brass has to go somewhere)

Tim, I have a small right angle scribe that comes with the RCBS Case Master tool (any sharped edged right angle scribe will work). Every firing, after I clean the cases and during inspection, holding the scribe in my fingers I run the point down the inside of the powder chamber. You'd be amazed at how you actually feel a valley forming from the inside as they start to thin out. Its a good way to monitor the heads for stretching. If the sharp point gets caught, you know that a cracks forming.

The RCBS Case Master makes it very easy to measure the wall thickness of the chamber V's the wall thickness of the stretched valley at the head.

Kinda thing...…. if you smell what I'm cook'n.

AlanF wrote:

Tim N wrote:

BRETT B wrote:Too many firings, Too much pressure, Oversizing case, Sizing Die is under size to chamber, leaving lube on case, not cleaning out chamber after cleaning,Over Annealing (IMO).

If the case does not grip the chamber wall it will grow and separate like you have .

Thanks for sharing all my reloading techniques...

So I may have done something wrong??

Tim,

Oversizing the case is the usual suspect for case separation. Do you measure base to shoulder before and after bumping? If oversizing is the culprit, you'd expect it to be accompanied by a lot of case length trimming? (the brass has to go somewhere)

I have measured them a few times and 2 thou was the amount I bumped them.

DenisA wrote:Tim, I have a small right angle scribe that comes with the RCBS Case Master tool (any sharped edged right angle scribe will work). Every firing, after I clean the cases and during inspection, holding the scribe in my fingers I run the point down the inside of the powder chamber. You'd be amazed at how you actually feel a valley forming from the inside as they start to thin out. Its a good way to monitor the heads for stretching. If the sharp point gets caught, you know that a cracks forming.

The RCBS Case Master makes it very easy to measure the wall thickness of the chamber V's the wall thickness of the stretched valley at the head.

Kinda thing...…. if you smell what I'm cook'n.

Thanks Dennis
I’ll try the paper clip method mentioned in a previous post which is just the cheap version of your scribe

Only the case master allows the measurement

For some reason, many people shun the simple pointed bent wire scribe feeler as too simplistic. Can I suggest that it is actually more practical than sophisticated gauging in simply detecting cases heading towards separation.

It is a vital piece of gear which should be on every reloading bench.

Peter Smith.

Being able to detect the thinning is one thing but then how do you manage it if you dont know how thick the brass is at that point? Or do you just throw the case away when you first detect it?

DenisA wrote

Being able to detect the thinning is one thing but then how do you manage it if you dont know how thick the brass is at that point? Or do you just throw the case away when you first detect it?

You will soon develop a feel for that. Basically it should not be happening and there must be a cause. Usually bumping cases back too far.
You will also see a stress ring around the outside of the case eventually which incicates case head separation is becoming a risk.

Find a few example cases and keep them handy to assist with this. It is worth a club having some samples.

There is a possible complication with the SAUM case. For some reason, many have slightly thinner extraction rims than other cases. A LOT of force is required to withdraw a FL sized case out of the die - this can slightly fold back the extraction area. The base becomes dished. This especially true with some cheaper looser fitting shell holders. The end result is that the die is set to oversize cases.

Peter Smith.

Love reading your posts Peter

I tried the paper clip method which was easy enough.
The worst cases had a crack starting internally making them quite noticeable to the ones with thinning only which were easy to pick out.
Out of 300 cases I had to toss about 12.
The ring on the outside of the dodgy cases was a bit of a giveaway.