Old Model Super Blackhawks are highly resistant to frame stretching. My first large bore Ruger revolver was purchased new in 1972 for $125. I am approaching 35,000 rounds through it. Almost all of those rounds were reloaded to Skeeters favorite .44 magnum load (today considered over maximum). It is as tight as the day I bought it.
I once even did an experiment to determine what this particular revolver could really take. With 250 grain cast bullets I started at 24 grains of the old 2400 and worked my way up in half grain steps until I saw flattened primers and hard case extraction. I got to 29.5 grains before I saw unacceptable pressure signs. The blast and recoil was impressive.
While I do not recommend anyone try this experiment, it shows the high safety margin in Ruger revolvers.
I too have a second generation Colt SAA in .357 magnum. Out of respect for the rather delicate top strap, I have mostly fired .38 specials in it:
I always use lighter loads in my old model .44 magnum flattops:
John