I'm relatively new to reloading and for the first time I have several load/firing cycles on a batch of brass.

Here is a photo of one of my 375H&H cases, the life of which has consisted of:
- initial full length sizing
- 4 firings for load development, neck sizing between each (hottest load was prob 77grs of Win760)
- 5th firing with 75grs of W760
- Full length sized (bolt was getting hard to close after the 4th firing)
- sectioned the case to see what was going on


Is this batch of 5x cases ready for scrap or is there any life left in them? Is there any amount of wall thinning that is acceptable?

This looks like the classic pending case head separation.
A bit unusual for "neck sized" cases. So I am interested in other options/opinions.
As to your question of scrapping the brass, I would pitch them. Brass is cheep compared to the damage that uncontrolled escaping high pressure gas can cause.

muck

Personaly I`d scrap them, but 5 loads is not excessive IMO.

take a new case, use a standard load, fire, and cut in half...

That case would probably separate with one or 2 more firings.
If you want a real education get or borrow a .303 British Lee-Enfield and try a few reloads. You will probably start getting complete head separations by the 3 firing. I have picked up .303 once fired cases that had impending separation after firing the factory load.

Like most chambers for belted magnums, I'll guess that yours is on the "sloppy" side. I wouldn't be surprised if the largest portion of the pressure ring you now see didn't manifest itself on the first firing of the new case.

The brass that is "absent" from the pressure ring about a quarter-inch in front of the head had to "go" somewhere. How much trimming has been necessary in these five firings?

Typically, a case that is somewhat sloped and has a minimal shoulder (like the .375 H&H) is conducive to brass flowing forward upon firing, causing an increase in the length of the case ("case stretching"). I would guess that five to six firings is fairly good life for a .375 H&H if the loads are "full power".

quote:

Originally posted by muck:
This looks like the classic pending case head separation.
A bit unusual for "neck sized" cases. So I am interested in other options/opinions.
As to your question of scrapping the brass, I would pitch them. Brass is cheep compared to the damage that uncontrolled escaping high pressure gas can cause.

muck

Looks a little like the chamber is oversized.
Neck sizing shouldn't mean squat since the belted magnum cases headspace on the belt!

Don
here's what I think .. which could be wrong.

once fired, the case fits the chamber .. neck sizing a belted case works EXACTLY like neck sizing a rimless case, as it headspaces off the shoulder NOT the neck ...

however, the case is blown out and filling the chamber.

I get less reloads per case with my 375HH than any other rd. and I only neck size. I think it is the long tapered case with not alot of shoulder.

I find the same thing with my 300 wm about 5 rounds and I can find case thinning.

Didn't have any virgin or 1x brass, but I sectioned a piece that had ben fired twice. This one would have been full-length sized before first firing, and neck sized twice.

So I don't think I have an overly large chamber.

I got in the habit of trimming cases after every use (using the Lee case lenght gage/trimmer). Can that contribute to excessive stretching?

Or is 5 uses out of a 375H&H case about what to expect with full-power, non-max loads using neck sizing?

That case looks great .. remember, 5 reloads aint bad case life .. try setting your neck sizing with imperial lube..

better.. does a fired case, unsized, fit right back into your chamber, with teh same resistence as a neck sized one?

Do not resize FL before the first firing. If at all, only neck size.
Use a sissy load for the first firing and slightly lube the front half of your case. This will keep the shoulder area from sticking to the chamber and case lengthening will be distributed over more or less the full lenght of the case, not just the narrow part above the case head.

When FL resizing is indicated, resize only as much as is necessay. Anything more will again create excessive headspace and induce case thinning upon the next firing.

Oh, and case trimming has absolutely nothing to do with case stretching. It merely cures the results of it.

Mr. Fox is correct.

It's poorely under stood that the firing pin strike and primer detonation drives a case one or two thousants deeper into the chamber no matter how it's been sized. Chanber pressure then (usually) seals the case against the chamber that the thinner fordward end is locked to the chamber. Increasing pressure drives the thicker rearward case firmly against the bolt face, stretching the wall and thinning the web as you have discovered.



"Full length" sizing fully repeats that cycle each time, until the case ruptures or is tossed. Some rupture with three reloads, some with five or six.

Properly sizing, so the case is "headspaced" off the shoulder with minimum slop will provide best case life because it experences the least posible stretching.

Cases with a wide, sharp shoulder are more resistant to being driven deeper into the chamber much better than those such as the old .375. You're going to get some stretch each firing no matter how you resize.

What you're experiencing is absolutely NORMAL for a 375H+H, due to it's long sloping case and minimal shoulder.
Upon firing brass is flowing forward just ahead of the web. No sizing method can reduce this in this instance, because the firing pin blow will push the case forward until the belt stops it, then when full pressure is reached, the case walls grip the chamber and the brass is stretched rearward until it contacts the bolt face.
Brass is also flowing into the neck, I've measured trimmed brass before and after firing and found lengthening in the region of .040" (1mm).
4-5 loadings is all you can expect from this round, unfortunately.
I remedied mine by having it re-chambered for the 375Weatherby, neck lengthening and case stretching has been practically eliminated, and I FL size all my brass.
Hope this helps.