I have never shot a Raging bull, and haven't read of any analysis of the Raging bulls metalurgy or design. There have been many pot shots taken, basically summed up that it's a cheap imported gun.
There have been reports that both Taurus and Ruger have shipped guns that were poorly assembled and that didn't shoot worth a hoot. I haven't heard any qualified statements that either guns have catasrophically failed in use. I have heard of some Raging Bulls shooting loose, I've never heard of a SRH shooting loose.
The metal used in the SRH is likely much stronger then the Bull, however, the SRH cylinder is much thinner, and has cutouts over the chamber, so they have to be made of stronger metal.
I know that a few brave, or more accurately foolish soles have had SRH 480's rechambered to 475 Linebaughs, and they've pushed the loads to the limit, ie 400 gr @ 1500 fps. Those guns haven't broken, but the shooters say the guns are unshootable at that level of recoil.
I've personally put several thousand rounds through my 480, evenly split between max loads and mild loads. The gun is as tight and accurate as it was new. I've even put a few loads through it that were too hot and caused the cases to stick.
Now to the question of only using factory ammo. It is a CYA statment by the factories. They have no control over what sort of handloads are run through there guns, and a careless handloader can certainly assemble ammunition that will damage or destroy a gun.
Handloading is potentially dangerous, and requires care and prudence on the part of the handloader. I haven't fired any factory ammo through my 480, nor do I ever plan to. It is my choice, and I have to live with the consequences of my choices.