I'm well familiar with the concepts of barrel harmonics, and precession and their effects on short and long-range accuracy.
There's another, somewhat more practics, way of examining the abilities of the 1903 vs. the Lee Enfield at long-range...
The results of the various Palma and other matches held between the United States and Commonwealth countries in the first half of the 20th century.
The United States won 6 of the 7 Palma matches held when the US teams were shooting 1903s vs Lee Enfields.
Generally, other international long-range matches also saw US shooters holding a significant competitive edge over their Commonwealth opponents.
Additionally, that article is from 1901.
Kind of hard to say that the Lee Enfield is categorically more accurate than the M1917 or the M1903 at long range when: A) those rifles hadn't even been designed/adopted when that article was written, nor had "modern" bullets been developed for either rifle.
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