I am 53 years old, short-sighted and wear wide-view, graduated lenses in my glasses. I shoot a variety of old Winchesters in a variety of calibers and all of them have open iron sights with the exception of the 30-30, which has a receiver peep sight. I probably only shoot 20-40 rounds per week in the spring, summer and fall. I develop my own loads, and once I have an accurate load, with the forearm resting on a block of wood with a pad on top of it, and holding the butt to my shoulder with my left hand, I can easily and consistently get 5-shot groups that are between 2 and 3 inches. Anything over 3" I consider to be poor shooting on my part. With some of my guns, if I'm shooting in the morning when my eyes are fresher and the sun isn't shining on my target, I can get 5-shot groups as small as 1 & 1/2 inches. I have occasionally gotten 3-shot groups of slightly less than 1" at 100 yards, but I consider a 3-shot group to be cheating .... a five shot group is more indicative of shooting ability. All of these groups are with cast bullets. Offhand, it is another story. I can regularly get 1.5" 3-shot groups at 50 yards, but I find 100 yard offhand shooting much more difficult. I need more practice here, but I can get five shot groups of 4.5 inches, but not consistently. This is not so much a matter of the sights, but of practice.
Here's a typical 5-shot group from a 104-year old 45-70 shooting plain base cast bullets at 100 yards, using my most accurate load for that rifle. The rear sight is an open leaf sight, with a very wide notch, which I find more difficult to shoot accurately with. Forearm was resting on a block of wood with a pad on it and butt was held to my shoulder with my left hand.
Here's a 5-shot, 100 yard group shot with an old Winchester 44-40, semi-buckhorn sights. This is one of my more accurate rifles:
Here's a 5-shot group, 200 yards, with an old 38-55 with semi-buckhorn sights, shooting undersize bullets. This is not an accurate load, but you see what iron sights will do with a under-performing load at 200 yards. The vertical string is probably also exaggerated by the front sight, which someone sharpened almost to a knife edge and I'm never exactly sure where the tip is.
Here's a 4-shot group shot offhand at 100 yards with my 45-70.