Howdy
I have owned a couple of Uberti Cattlemen over the years. The one I have now is about 15 years old, so I cannot speak for what they are making today. I just ran downstairs and measured the cylinder throats. Using my calipers, the throats were running around .453-.454. However, a caliper is not the ideal tool for measuring cylinder throats.
The old standard is, the correct bullet for the throats will just pass through the throats with a little bit of pressure. If it falls right through, it is too small, if it needs a lot of pressure to be shoved through, it is too large. A .452 bullet (which is standard for 45 Colt) pushed through just right with light pressure.
Regarding pushing 44 Mag pressures with a gun built with basically the same dimensions as the SAA, forget it! Perhaps you have read about Elmer blowing up a Colt with high pressure loads. That's why he went down to 44 Special when he eventually developed the 44 Mag. Any 45 caliber revolver is going to have thinner cylinder walls than the same gun chambered for 44 caliber. The Uberti guns are basically dimensionally the same as a Colt, they are not designed for hot loads. Personally, I would never push any revolver built along the lines of the SAA with anything more than SAAMI Max 14,000 psi loads. These guns are not 'old model' Vaqueros or Blackhawks, they are not as massive.
Do not confuse a 250 grain bullet moving at 800 fps, the factory standard load for many years, with 'cowboy powder puffs'. Far from it. That load was the most powerful factory load for revolvers until the advent of the 357 Magnum in 1935. It is still plenty potent.
Regarding accuracy and fixed sights. Do not confuse Point of Impact vs Point of Aim with accuracy. Accuracy consists of how small a group a gun will make, not where it puts the group. A 45 Colt with proper ammunition is plenty accurate. It will make a small group. Kentucky windage and experience will put the group where it needs to be if it is not exactly where it is desired.