No. 4 Rifle; Zeroing Instructions Data Inconsistency?

[Surpmil]

100 years after its introduction do we still consider the Lee Enfield Action to be of unsound design ?

In the Lee action the bolt-head does not rotate with the bolt, but the lugs are disposed at the rear of the bolt cylinder. This is not a desirable arrangement as, on firing, the greater part of the body and bolt are thrown into a state of tension and compression respectively. This strain, acting on the unsymmetrical central part of the body, causes lateral vibrations, which have to be compensated for by displacing the foresight laterally. The unsymmetrical incidence of the strain also has a disturbing influence on the accuracy of the rifle. The British action has, however, advantages which may compensate for the fact that, mechanically, its design is unsound. There is no deep cylindrical portion in front of the action body as in the continental forms, in which dirt can accumulate. The form of the action and the shape and disposition of the bolt - lever allow of extremely rapid
fire.

What's the source of the quote? It reads as though it refers to the days of the Lee Enfield Mk.I and the sighting problems detected in South Africa(?)

The tests recounted in the same TBSA 1929 remind us that where chamber wall adhesion occurs in firing without the presence of oil, grease or water to interfere there much less back pressure on bolts and bolt heads than we tend to assume. I can't find the text from TBSA at the moment, but here is an article posted by Ed Horton in 2009 that goes into some detail: Rifle Chamber Finish Friction Effects on Bolt Load and Case Head Thinning Calculations done with LS-DYNA

Chamber wall adhesion alone tends to negate the oft expressed concerns about the strength of the action and its "unequal" proportions on either side. The importance of dry and clean chambers and ammunition seems not to be as widely known as it should be however.

The flexibility and resulting "compensation" turned out to be advantageous.

Overall events have proven that J.P. Lee and his later assistants did a fine job, though it certainly took a long time to incorporate some of the later improvements.