The most common grain bullet most people use for deer hunting in both cartridges is 100 grains. If you can tell the difference on game between the two, your imagination is better than mine. I've used both and I sure can't. Now if you move up to 120's in the Roberts I suppose you would maybe see a difference, but most Roberts don't shoot them as well as 100s.
The problem I see with the Roberts is it's a "tweener", a little long for a short action, and a little short for a long action. I have also found the .243 to be more accurate, or shall I say easier to find accurate loads. I think the only real reason people like the Roberts so much and tout it as better than the .243 is they simple think the name is cool. They just love to call it by it's nickname "Bob". It's a cult thing.
I think you uncle was right, if you want to see a power difference get a .270 winchester.
