S&W 45 w heavy loads
The S&W top strap will NOT stretch. That's a myth.
What does happen with abusive loads is that the tail end of the yoke tube wears a groove in the bottom of the cylinder well allowing end shake to develop. This is the Achilles' heel on the S&W. Why they don't fix this once and for all I don't know. It would take a rather minor design change.
If you have a hand grenade type load the cylinder will generally fail at the web between chambers. This type of failure will progress and result in the opposite web on the same chamber failing, the wall of the chamber and half the wall of the adjacent chambers is then blown off, taking the top strap with it.
It's not likely to fail at the bolt notch, that's another myth. If it's a 45, I have heard of the bottom of the notch bulging, but not failing.
Years ago I saw a test which attempted to lay this myth to rest. Starting with an N frame 357, one chamber was ground flat even with the bottom of the bolt notch for the entire length. A second chamber had a slot the width of the bolt notch cut the entire length. The revolver stayed in one piece when both chambers were fired. Next a barrel with NO bore was installed. Again the revolver stayed together when fired. (Note that bore obstructions are generally not close to the bullet and allow it to get up to speed before it encounters the obstruction.)