I've noticed that we have 93+ posts on the topic of calculating pressure, but only two people have posted to Auke Bay LT's question about case head seperation.

Since the issues are often related, can some of you pressure experts please take a few moments to help the Lieutenant with his question?

Well to be honest...

I did not even know a revolver could have Case Head separation...

So I just stayed out.

Same here.

My case head separations were in bottle neck cartridges caused by over sizing, not by too much pressure

How does a pistol case head separate?

Yes straight wall cases can separate in a revolver.A well used , reloaded many times case can indeed separate. This is why you should always check cases for thinning walls and discard those that have seen better times !
I was asked to help with a jammed revolver at a range.I took a bit to figure out what the problem was. The front half of the case went halfway into the forcing cone and half stayed in the chamber .Bullet went to the target .Finally figured it was separated so it was hammer time ! Finally got it out with the mallet and a lecture to the shooter - check your cases !!

The mechanism of case head separations are as follows:

1. A case is fired and expands to fill the chamber. The sloppier the chamber and the higher the pressure the more it will expand.

2. The case is resized. In doing so it is squeezed together and the brass thus squeezed has to go somewhere. The more it has expanded, the more brass will be squeezed toward the case mouth. The path of least resistance is toward the mouth of the case and not toward the head where the brass is much thicker.

3. Since brass is essentially flowing toward the mouth of the case, there is loss of brass thickness near the head and finally a head separation.

4. Aside from the above, brass can stretch more from excessive head space and from case design. Long tapered cases like the 375 H&H Magnum are more prone to stretching than cases with less taper.

Since the issue is related to resizing, high pressure will contribute to it since the case expands more and thus needs more resizing. Likewise, if the chamber is a bit sloppy, the case will expand more and predispose to head separations.

Straight walled cases are least prone to stretching and since many are fired in guns loaded to lower pressures, are much less prone to case head separations. Head separations can happen though even in straight walled cases. A case in point (pun intended) is the load I shoot in an Encore 460 S&W Magnum which is probably approaching the SAMI maximum of 65,000 psi. Brass with that load lasts maybe 3 reloadings before the groove at the web starts forming and if I try for 4 or 5 reloadings, a head separation will occur.

Case HEAD separation usually happens at or near the junction where the case solid portion starts...while CASE separation in straight walled cartridges can happen more toward the center...but I've had cases separate at various points up and down the case walls from just below the crimp zone to just above the base sizing zone and each time it was with a different case/caliber.

The problem is...case HEAD separation can usually be readily identified and usually well prior to the head coming off but not so with CASE separation...that happens at a weak point decided by many factors like chamber dimensions, shape and condition...where the mose sizing occurs, caliber, pressure, number of reloads, sizing die fitted or not, brass or nickel plated...etc.

Straight walled cases thin out fairly uniformly and evenly all over the case walls...MOST OF THE TIME...and you need to use a tubing mike on the new case to find the original thickness, then mike after each 10 or so firings or keep track of the total amounts you trim...after you trim 0.030" tp 0.050" total you can be sure the case is on it's last legs...that trimmed brass had to come from someplace.

Ive reloaded the same case in 38sp/375, 44sp/44mag, 444M, 45-70 anywhere from 30-60 times depending on the caliber and load just to see how long the case would last(and the same with 223 and 308) and after I said "enough", I couldn't tell a difference visually...outside and with a light shining down into the case...between the first and last shot.

The only difference was ~0.002" in case wall thickness in the 444M and the 45-70 between the first and last shots. That is with sizing dies that are fitted and only move the walls about 0.001" during resizing.

I keep those cases on my desk as reminders of how case life expectancy can be increased by using fitted dies with bushings.

It isn't pressure per se that kills a case(except getting well over the pressure limits of the brass metal itself), it's the amount of movement of the brass during the resizing/firing cycle...which work hardens the brass and makes it brittle.

Using fitted dies, annealing the brass, UNIFORMLY(have someone with an annealing machine do it), after some number of firings and keeping the pressure within reason and 100 cases will out last several barrels.

This is what I have observed generaly speaking, but as par for the course...nothing is ever general so the only way to find out is to do some experiments yourself and document your findings.


Luck

My experience with straight wall cases is they usually split length wise in the middle after many, many reloads. if the die and chamber were fitted the case would last even longer and would probably split at the case mouth.
Of the cases I have reloaded repeatedly I will often have the primer pockets wear out from repeated priming and repriming. They do not get loose from pressure, they get from mechanical wear.
If cases are separating because of high pressure the answer is obvious. Reduce the load.