A 2-inch group at 100 yards with open sights would indeed be especially accurate!

If we are talking scopes, on the other hand, accuracy should be similar to rifles today.
For example, the 105 year old open-sighted Rigby .275 I am playing with at the moment is under 2 MOA with most loads, so long as I can see the target!

At some point I intend to get my .280 Ross shooting, despite the difficulties of making cases and acquiring bullets. Happy to report accuracy on this forum when that eventuates.
Frankly I have difficulty believing the statements above, unless TW's 'factory' ammo was loaded with normal 7mm bullets, in which case his comments are quite understandable!