Not a metalergist but you have to define "stretch". I think of a rubber band with the word stretch. How much does a frame stretch with each firing and I suspect the frame has some elasticity designed into it but all in all it would take a long time and a very large ammo supply to get measurable results.
My thought is that the forces on the revolver frame should be under the elastic limit for the frame material. So...it really should not "stretch" in the sense that it becomes longer permanently. It should take loads over the cartridge limits to do that kind of damage.
So for a good stainless steel revolver, if shot enough rounds will the frame eventually crack?
Most people who talk about "stretch" and other matters involving fracture mechanics don't have much of an understanding of what fracture mechanics is and what it involves. In fact, even those who do have an education in the subject may only understand the basics sufficiently to understand a specific application as opposed to the kind of understanding that others who dwell in actually determining the actual values for all the various parameters that go into it for any given material sample and then how that material is actually used in specific applications.
Fracture mechanics is the study of crack propagation in materials and uses various analytical methods to quantifiably define certain characteristics of the material. There are various simple tests that could be discussed, but it rapidly gets very complicated the deeper you go.
Here are a few terms:
Fracture toughness. Put simply, this is a material's ability to resist crack propagation when under a tensile stress by plastic deformation. Bending, in other words, instead of snapping.
Tensile stress. This is a stress that is felt when under tension, or when a force is applied which pulls a material apart (stretches it).
Compressive stress. This is a stress that is felt when under compression, or when a force is applied which squeezes the material together.
Brittle fracture. This is the sudden, catastrophic failure of a metal with a pre-existing flaw when under a tensile stress with little or no plastic deformation. Basically, it "snaps".
Ductile failure. Failure of a metal under stress by plastic deformation. It "bends".
Creep. A metal deformation that occurs at stresses below the yield strength of a metal, usually under elevated temperatures. It's a form of plastic deformation.
In general, very hard materials are very strong. But when they DO fail, it's with little warning and it's a catastrophic failure: It snaps. Such materials are said to have a "low fracture toughness".
To complicate things, a material's ability to resist failure by either plastic deformation or by brittle fracture can change over the life of the material. Here are a few reasons:
- Cyclic stresses. Materials that have a high amount of cyclic stress will change the size of the pre-existing flaws (cracks) with the metal's crystalline structure. This changes the metal's fracture characteristics. Cyclic stresses can be caused by physical application of tensile and compressive stress by various means, or by cyclc temperature, for example.
- Material temperature. Heat/cold can directly affect a material's ability to resist brittle fracture or plastic deformation.
- Damage to the material. This can be caused by physical means, such as dropping, impacts with other hard objects, cutting, etc. Anything which either deforms, cuts, corrodes, chemical contaminates, or introduces/enlarges cracks in the material.
Quantifying the stresses any given piece in a structure sees is exceptionally difficult. Hell, it's borderline magic. In many cases, such in depth studies are not required. But for components and structures that are approaching physical limitations, it's very important to understand these stresses in order to ensure they are not exceeded during their design lifetime. Otherwise you get something like what happened to the SS Schenectady (picture below), a brand new ship built in WWII which literally broke in half after sea trials while tied up next to a pier.
OK...now with all the really cool engineering mumbo-jumbo behind us, the good news is that any quality firearm built, when operated within its design limits, should have a cyclic lifetime that is measured in decades, and even generations, of normal use...even very heavy use. By the time you get to any kind of structural failure point, you will have LONG SINCE "gotten your money's worth" out of the firearm. Like a car or truck, some minor failures will likely happen at some point. If you have it long enough, you may simply "wear it out" in some way. Sometimes the minor failures or wear issues can be repaired and you can add many more years to the life of the firearm. Even so, nothing lasts forever and if you use it long enough EVENTUALLY it's going to fail in some manner which will make it not worth repairing.
So my opinion is to simply take care of your firearms as you would normally, which includes cleaning, lubricating, not abusing them, not loading ammunition beyond established standards, etc. And have fun shooting them as often as you wish.
SS Schenectady picture I promised: