Thompson/Center's Contender pistol has held the world record for about 20 to 25 years. The group was fired at 500 yards, using iron sights. I believe the group measured .75" X 3.5". For what it's worth, ALL T/Cs come with an MOA guarantee...handguns, carbines and rifles.
Re: the advantage of any single-shot, when you have one shot, and you know you have one shot, you practice, and build your confidence. Confidence. : ) That's the advantage. Patience. That's another.
I have heard many good comments of H&Rs. I have not personally fired my own .30-30 that I bought LNIB. She's sure pretty. Nice classic lines and takes my mind back to days when I was 8 Y.O. and hunting with single-shots. Wow, those are some great memories.
Geno