And brass is stronger than steel?
Ever done a burst test on a steel pressure vessel? You fill it with water, and increase the pressure until it bursts.
If you think that makes water stronger than steel, than I can see how you would think that brass is stronger than steel.
The brass in the chamber stretches under pressure (that's why you have to resize brass to reload it, and why you can fire-form cases to different calibers).
Think of the brass like a balloon in the chamber. I can put a kid's plastic toy balloon inside a closed steel chamber and keep increasing the pressure until the steel bursts. The ballon can easily stretch more than the steel, so it just expands until it's steel support goes away then immediately bursts itself from the internal pressure. Doesn't mean that the plastic ballon is stronger than steel.
Same thing happens in your firearm's chamber. Once the brass stretches to the wall of the chamber, now the pressure is trying to compress the brass, and all the load is reacted by the steel chamber wall. The brass and steel keep stretching together at this point, until either the bullet leaves the barrel and the pressure drops, or the pressure keeps increasing until either the brass or the steel fails catastrophically.
If the brass fails first, it will generally fail in the area unsupported by the feed ramp and blow the magazine apart as you described earlier.
If the brass is supported by steel behind it (fully supported chamber), it can keep stretching until the steel chamber comes apart around it (like the pictures of the .45 I posted above). Once the steel chamber walls come apart the thin brass can obviously not withstand the pressure by itself.
Every time you fire your gun, the steel chamber stretches slightly the returns to it's original size. This is the primary reason you do not want to fool with home heat treating your gun. You could easily make the steel hard and brittle enough that relatively few cycles will cause it to fail, kind of like trying to bend a file. The file is like a piece of glass, very hard but brittle. If you're looking at material properties, it's yield strength is the same as it's ultimate strength. Those aren't the properties you want in your firearm chamber.