As I noted in an earlier post, I have Pietta Brass framed Remington 44s, The 12 inch Buffalo gun is still doing just fine and I dont shoot wimpy loads but keep them reasonable.Ditto for the 9 inch. I dont know how heavy a load others are shooting to stretch the frames but no stretch on mine. Calipers show everything is still tight and where it should be. My normal load is 24.5 to 25G of 3F depending on weather and humidity! So what are loads are people using that have stretched frames? Thanks
25 grains seems to be a fairly reasonable to maximum load of 3F for a brass frame Remington and shouldn't cause any problems for a very long time if at all.
Some folks have shot 30 grain loads but perhaps not for enough shots to cause any noticeable damage.
It's not really known how much powder can be loaded and for how many shots before any damage can occur.
With the Remingtons I've heard that the cylinder pin hole in the recoil shield can become oval over time which can affect the alignment of the cylinder.
But I've never heard anyone actually quote any statistics about how many shots were loaded or with what specific powder charge before they noticed any harmful damage.
Someone would probably need to keep track of all of the shots that they took over the lifetime of the gun up until they noticed any damage to help determine the trouble free lifespan of a gun.
But then each gun and circumstances may be different based on the individual gun, the actual type of powder & ball size used and the loading method.
One would think that the larger the powder charges, the more risk to the frame, and loading the cylinder off the frame would also reduce some of the stress on the cylinder pin and some of the risk.
Sorry that I can't be more help answering your question with any certainty or hard data.
But I did want to mention what I believe to be some of the variables involved.