flattail:
Can only advise you as to what I have done with the older H&R 44 mags (casehardened frames). I have owned and handloaded for several since the 1970s. I loaded to the factory levels as far as pressures are concerned and have never had a problem. But..I am not aquainted with pressures of the Buffalo Bore loads. If they are loaded beyond the factory levels, they might stretch your frame. That is the failure point of these old frames. Once that happens, the frame is shot. But, this form of failure is prefered to the gun coming apart.
My advice is to respect the age and design of these fine old guns, and enjoy them as they are with factory loads. If you need more, sell the old timer, and get a NEF SB2 in 44 Mag. The price you get for the older model (if it is as you describe) will pay for the new 44 Mag. There some fans of the old models (like me) who is always looking for another. Good luck.