How will my cases fail and when?

[nksmfamjp]

So, I have a 300 Sherman on a Win 70 action…

I formed with a false shiulder
anneal each time
FL size to min headspace
Case has 40 deg shoulder
Trim each time
Necks have 0.0035" clearance on diameter
about 0.002" neck tension
Warm loads seated to lands - 0.040"

So, when my cases fail, how should I expect them to fail? At about how many firings?

When I was less careful, split necks caused my failures.

 

[JMW67]

I would have to guess it will be primer pockets failing first and as far as how many firings you get will be determined by brass manufacturer and how hot the load really is. Take one piece and shoot over and over till it fails and this should give you a good idea of whats going to happen

 

[SDPlinker]

 

[257 STW]

I would have to guess it will be primer pockets failing first and as far as how many firings you get will be determined by brass manufacturer and how hot the load really is. Take one piece and shoot over and over till it fails and this should give you a good idea of whats going to happen

 

[Stammster]

What headstamp brass?

 

[257 STW]

IMHO what you are asking is going to be dependent on how hard your pushing your brass (hot loads) I have even seen people only get a few firings from Lapua, ADG brass if your way hot. PPs are usually the first thing to go. And I am speaking in general terms, as I have no experience with the 300 Sherman. my .02

 

[PddPdd]

Also, how much you work your brass when resizing will have an affect on case neck life.

As far as splitting the necks the following options would affect brass life but less so since your are annealing between firings. After firing, how do you resize your brass? In order of most to least working of brass"

1) Factory FL or neck only resizing die with factory button inside?

2) Custom FL or neck only die with stem & button removed to minimize resizing reduction in diameter, then size with a mandrel? It still has to work with various neck thicknesses.

3) Bushing dies where you only reduce the neck enough, based on neck thickness, so a mandrel still has something to enlarge to reach final desired "neck tension".

Note: I have not tested these options with annealing to see if annealing makes all of these options equal in terms of case neck life.

Of course primer pockets may still be the weakest link and fail first depending on how "warm" you are loading.

 

[FreddyG]

Unless you have max or near max loads, the primer pockets won't go first. You will get case head separation. That is how they will fail, because each time you bump the shoulder, brass grows. The growth depends on how much you bump the shoulder.

If you neck sized only, the primer pockets will fail before anything else, provided you still anneal.

 

[MagnumManiac]

Unless you have max or near max loads, the primer pockets won't go first. You will get case head separation. That is how they will fail, because each time you bump the shoulder, brass grows. The growth depends on how much you bump the shoulder.

If you neck sized only, the primer pockets will fail before anything else, provided you still anneal.

These 2 statements are so far from fact that it defies logic.
Have you never seen a neck sized case fail to chamber??
The cause is from the case STRETCHING each time it is fired to fill even more chamber…..the only remedy it to SIZE it so it fits again. No different to partial FL sizing that actually prolongs case life, not shortening it.
In most cases with long case life, it is not always the primer pockets that go first, but the case becomes difficult to size near the web and no longer chambers, well before the primer pockets open too much.

Cheers.

 

[FreddyG]

These 2 statements are so far from fact that it defies logic.
Have you never seen a neck sized case fail to chamber??
The cause is from the case STRETCHING each time it is fired to fill even more chamber…..the only remedy it to SIZE it so it fits again. No different to partial FL sizing that actually prolongs case life, not shortening it.
In most cases with long case life, it is not always the primer pockets that go first, but the case becomes difficult to size near the web and no longer chambers, well before the primer pockets open too much.

Cheers.

Not everybody pushes the envelope. Cases that are neck sized only, with mild to medium loads, don't fail to chamber.

If your neck sized cases fail to chamber, you are pushing your cartridge past it's designed limit, period. Same with loose primer pockets. They loosen from exceeding design limits.

 

[Ucsdryder]

How would one know when the primer pockets or going or gone?

 

[FreddyG]

Resistance when seating a primer. Some fail to hold a primer after running hot loads.

 

[MagnumManiac]

Not everybody pushes the envelope. Cases that are neck sized only, with mild to medium loads, don't fail to chamber.

If your neck sized cases fail to chamber, you are pushing your cartridge past it's designed limit, period. Same with loose primer pockets. They loosen from exceeding design limits.

Ain't so…..but carry on.

Cheers.

 

[FreddyG]

Ain't so…..but carry on.

Cheers.

If you actually tried to do what I posted, you would quickly agree.

Take the 6.5 creed case for example, a large primer pocket case will take less abuse over the small primer pocket case. Different design is what dictates failure points. You can run the small primer pocket case much harder.