George E. Frost, who worked in the ammunition manufacturing industry for decades, wrote a book about the subject, Ammunition Making, published in 1990 by the National Rifle Association. A considerable part of the book has very good information about .22LR ammunition.
In chapter 10 "Troubles" there is a section on Burst Heads on pages 112 - 113. It may have relevant information and is reproduced in part below.
Burst Heads in Rimfire
The worst of all rimfire casualties is a burst case head. High pressure gas, escaping through the burst section, comes back through the firing pin hole and around the bolt, carrying with it small fragments of brass and burning powder. The magazine and stock may be damaged, the extractor blown out, and, worst of all, the shooter may be struck in the eye or on the face with brass fragments. The burst makes a loud bang close to the ears which is most unpleasant. Frequently, though not always, the bullet is left part way along the barrel by the sudden drop in pressure. With the bullet left in the barrel, a following shot will surely ring the barrel, producing a visible bulge. All of these things are bad. What causes a burst head? Some of the causes are:
High pressure
Heading defect
Thin, soft brass
Headspace
Sharp chamber mouth
Lack of head support
Revolver design, as regards the cylinder
Failure to fully close
The burst head may be complete, in that the head is entirely separated from the case, or the break may be partial, with only a portion of the head blown out.
Examination of the burst may give some clues as to cause. With excessive headspace, a complete separation will leave a short section of the case body in the chamber. Comparing this short section with the straight portion of an unfired case will show an obvious length difference. The burst under normal headspace would show a straight portion the same length as that of an unfired case. Likewise, a partial burst from too much headspace will show a head of peculiar thickness, almost like a double head, and a short body section. These causes are easy to spot.
What has happened is that, as the pressure starts to rise, the case is forced back against the fact of the bolt, pulling the body of the case out of its full depth in the chamber. Brass is thinner in the case wall than in the head, and gives way as pressure rises to its maximum.
This burst is not the fault of the cartridge. In semi-automatic rifles, a failure of the bolt to fully close creates the effect of too much headspace. The symptoms are the same and the evidence will be plain to read. Failure to close fully is sometimes caused by mutilation of the case during feeding.
A rifle chamber must have its mouth rounded to a smooth, even if small, radius of .005" to 0.10". If the chamber mouth is left sharp or rough, the case will shear against the sharp corner under pressure. This can be spotted on the burst case by the sharp comer showing at the point where the case burst.
Sometimes the extractor cut on the barrel chips out or gives way. This leaves the case unsupported at that point, and leads to bursts. Again evidence will show on the fired case.
If too much of the face of the bolt is cut away and corners are left dead sharp, the general effect is almost the same as that of too much head space. The head swells back where there is no support and shears against the sharp edges. This situation is one of degree, and assignment of cause is not clear cut. A cartridge on the high end of the normal range of pressure may burst on occasion, while those of slightly less pressure will stand the strain. ...
Speak of a burst head, and most shooters will instantly think of high pressure or too much powder. The foregoing causes were discussed first to emphasize that the causes aren't all that simple.
If the case bursts because it isn't strong enough to withstand the interior pressure, it can always be said that pressure is the cause. Going a step further, it could also be said that firing the cartridge was the cause. The question is whether the pressure was within normal limits.
If the factory stays within the SAAMI recommendations for rimfire pressures (a maximum product average of 26,000 CUP) fewer than 3 rounds in 2,000 should exceed an individual pressure of 30,100 C.U.P., and those will not be much greater than this figure.
With this limit in mind, the factory, in establishing its basic case design, checks its cases out at pressures considerably higher than 30,000 C.U.P., so that there is a reasonable safety factor to handle the possible few which might reach 30,000 C.U.P.
Then, in production, working pressure levels are kept at average well below the 26,000 maximum allowable average, providing additional assurance that the individual safe high pressure limit won't be exceeded. Checks of pressure during loading are conducted, at least once or twice per shift. In
addition, powder charger limits are maintained by control chart. Lastly, the random selection and firing of at least one cartridge from each plate guards against any use of incorrect powder.
The net result is that pressures high enough to burst a normal cartridge case are extremely rare. No ammunition company wants to risk being charged with causing injury to its customers, hence the careful control.
Burst heads under normal pressure can occur, if the cartridge case is defective.
Most case defects causing bursts occur in heading. If the case metal is too thick, too thin or too hard, it may not bend correctly, creating a shear condition in the bend. This will show clearly in the shape of the burst portion.