I have heard that they are not as "strong" as the Blackhawk or SBH. What is the extent of the truth to this? I have read from several sources that the SAA in .45 Colt can only be loaded to a certain level and the Blackhawk can be loaded to a much higher pressure.
It is absolutely true, ...sort of...
The "sort of" part comes from the Ruger practice of using the same name, or very similar name for very different guns. Guns with different frame sizes, and strengths.
ok, lets be clear, when I say "Blackhawk", I'm talking about the "New Model Blackhawk", (post 1973 manufacture)
On the frame, left side, below the cylinder it says "New Model Blackhawk"
These guns use the "new model" lockwork, and are built on the .44 mag sized frame. This frame is larger than the frame size used by Colt for their Single Action Army (aka model P, aka Peacemaker), and its clones.
The reason for this is the difference in strength between castings and forgings. Castings must be larger to have the same metal strength as forgings. Ruger built his gun to be bigger, so the frame would be at least as strong as the Colt (and then I bit more, I suspect). The Ruger cylinder is a forging, just like the Colt and everyone else's. Because its made to fit in a larger frame window, it is larger than the Colt, and therefore stronger (more metal). (edit to add, since then, we have learned that Ruger's cast frame the same size as the Colt forged frame has adequate strength)
In the early 70s, handloaders found that the Blackawk .45 Colt would handle loads well above the factory maximum .45 Colt ammo (which was loaded to black powder pressures and velocities). These loads came to be called "RUGER ONLY" loads. At that time, there was only ONE Ruger .45 Colt model. Velocities and power levels matching the .44 Magnum could be done, but ONLY IN THE RUGER BLACKHAWK!!!!
Since then, Ruger has come out with other guns in .45 Colt, some which will take the RUGER ONLY Blackhawk loads, and some that will NOT!!!!
Ruger made a Colt style (fixed sight) single action they named the VAQUERO. It is the same frame size (and strength) as the Blackhawk. Still bigger than a Colt, but it looked like one. The idea was to make it more attractive to those people who wanted the traditional Colt LOOK. The VAQUERO will handle the hot "Ruger ONLY" load levels.
About a decade or so ago, Ruger dropped the VAQUERO and replaced it with the "NEW VAQUERO" it says "NEW VAQUERO" on the frame. It is a smaller gun than the Vaquero or the Blackhawk. It is the size of a Colt, and the looks of a Colt, and has the strength capacity of a Colt. It is NOT as strong as the Vaquero or Blackhawk, and is not rated for the heavy "Ruger Only" loads.
TO further confuse matters, Ruger has produced another size & style of frame, smaller than the new model frame, easily distinguishable by its "flat top". (it lacks the "hump" for the rear sight that is found on the new model frames), AND Ruger also named those guns "Blackhawk". They are not as big or as strong as the "standard" Blackhawk.
To help keep the confusion down, we call them "flat top models" but it is not an official name.
Now, as to what kind of power you need /want for hunting, that's up to you. The original .45 Colt blackpowder load ran a 250gr (255gr) bullet in the 900fps range, a little more on the higher end from longer barrels. People have been hunting (and doing other things) successfully with this load level since 1873.
Older reloading manuals, using COLTs as test guns max out a 250gr slug in the 1000fps range, depending on barrel length.
RUGER ONLY loads in the Blackhawk (the new model B, with the .44 frame) can drive a 250gr over 1200fps, with the extra power, and recoil that brings)
So, make sure what Ruger it is that you are talking about when you talk about strength and load level ability. It used to be simpler, today, not so much...
I realize its probably still as clear as mud, but I hope this helps some...
There's more to it, of course, and we're happily here to confuse you further, on request...