I had an old Speed Six .357
I had a Ruger Speed Six .357 with pretty bad holster wear and hard use. I bought it used and it was old, but I never had qualms about firing .357 Mag or any kind load out of it.
It handled .38 Specials as if they were cupcake loads. I fired Nyclad 125 grain +P; and there was little recoil and no concern for safety in using them.
In comparison--when I fired 125 grain .357's at night--there was a serious flash of burning gunpowder. The only thing that I was concerned about, was being night-blinded by that flash.
Your M66 should perform the same way, it takes a long time to wear out a good revolver. If I owned the gun, I would look it over pretty good and if it were visibly sound, I would let 'er rip.
Here is good way to tell if the gun is good: Check for cylinder alignment, by cycling the gun when empty.
Pull the trigger and let the hammer fall, the firing cylinder should always line up with the barrel. If it does, the gun is probably sound. If it does not, then you have a bad gun and that is a very bad symptom/indicator of one.
But, the relative strength of a good weapon is of little concern: Tuarus makes a good gun.