No. 4 Rifle; Zeroing Instructions Data Inconsistency?

[Rick]

Regardless, the 18x18 inch acceptable dispersion at 600 yards, effectively 3 minutes of angle, implies pretty clearly that many rifles, and whatever ammo was used to at least test them, were not of a high enough standard of accuracy to make the 2 inches at 100 yards under discussion here anything that could be relied on "in real life".

No, they tested in "real life":

Proof of Ball and A.P. Cartridges

19. Firing proof will be carried out by the following method :-
The number of rounds taken I or the proof will be 40 from
each make and date of manufacture. Two targets will be used,
20 rounds being fired at each target. Should a further proof
be necessary {see para. 31), the rounds required will be taken
from the same box from which the rounds for the first proof
were selected.

20. The rounds will be fired on a calm day by a marksman.

21. {a) Rifle ammunition and ammunition of a calibre applicable
to both machine guns and rifles will be fired from a rifle at the
shoulder, using either a table rest or an ordinary table with sandbags
resting on it: or in the prone position using a sandbag cover. Only
the forearm and wrist will be supported by the sandbags.

22. The 20 rounds for each target wilt be all fired from the same
weapon and aimed at the same spot on the target, the object being
to obtain a group of 20 shots fired as nearly as possible under the
same conditions.

23. The target will measure 6 ft. X 6 ft. and be ruled with horiz-
ontal and vertical lines 6 in. apart. It should preferably be white
in colour.

24. Three rounds will be fired into the butts to warm the weapon.

26. A marking disc, 6 to 12 inches in diameter as required. should
be affixed to the target to indicate the point to be aimed at; one
or more sighting shots should be fired, and, if necessary, the posit1on
of the marking disc changed to ensure the whole of the rounds
being well on the target..

27. The position o! the sighting shots, which will not be included
in the "Figure Of Merit". may be signalled.

28. The position of the remaining rounds will not be signalled,
and the marksman will not vary his point of aim during the shoot,
irrespective of where the shots may strike the target.

29. The position of the shots on the target will then be shown on
the diagram (A.F. B202) and the "Figure Of Merit" will be com-
puted in the following manner:

(a) Find the horizontal measurement--measure the centre of
each hit from the left of the target.
(b) Find the vertical measurement-measure the centre of each
hit from the bottom of the target.

Each of the above measurements should be made with a rule and
plotted in corresponding position on the diagram.
(c) Find the mean point of impact; find the total horizontal
measurements and the total vertical measurements, then
divide the totals by the number o£ hits on the target.
The quotients give the "mean horizontal'' and " mean
vertical " measurements. Draw a vertical line at a
distance from the left edge of the diagram equal to the
mean horizontal measurement, and a horizontal line
at a distance from the bottom equal to the mean vertical
measurement. The intersection of these two lines is the
"mean point of impact ", i.e. the centre of the group of shots.
(d) Find the deviation of each shot; measure the centre of each
hit from the mean point of impact, and for each miss
allow 5 feet.
(e) Find the "Figure Of Merit": add together the deviations
and divide the sum by the number of rounds fired. The
quotient is the ·"Figure of Merit.''

30. The ranges at which the various calibres are to be fired, and
the mean Figures of Merit are :-
Calibre Range Figure Of Merit
·380-in. Ball 50 yards 9 in.
9-mm. Ball 50 6
·45-in. Ball 50 6
·45-in. T.S.M.G. G. Mk. 2z 100 15
·455-in. P.S.L. and Revolver 50 10
·303-in. Ball 500 12
·303-in. A.P. 500 16
7·92-mm. Ball 600 12
7·92-mm. A.P. 600 14
·5-in. Vickers Ball 500 15
·5-in. Vickers A.P. 500 18
·5-in. Vickers S.A.P. 500 18
·55-in. Ball, Mk. 3 500 14
·55-in. Practice P. Mk. 2 500 18
·55-in. A. P. 500 18 "
15-mm. 500 18

31. Should the appropriate " Figure of Merit " be exceeded,
a second proof should be taken in different weapons. Should the
" Figure of Merit " of the second proof exceed lhe limit, the
ammunition should be provisionally sentenced unserviceable, and
the firing proof diagrams should, in this case, be forwarded with
the results of proof.

So... a marksman firing his rifle from a rest had to verify the proof of .303 ball with two targets, 20 rounds on each, with the Figure of Merit being they grouped inside 16" at that distance

A guess could also be hazarded that if this 8.5" related to anything else, it might be that it was thought preferable in zeroing practice and perhaps in combat to have the actual fall of shot slightly higher than the POA?

This percolated down from the same people who ran the School Of Musketry at Hyanthe.

And from the perspective of an infantry section or platoon commander, I can't think of a possible reason that would be desireable, rather than a true POA=POI when the sights are set at the correct yardage to the target. If you're going to argue about sighting so that the result is like aiming off, you would rather rounds were low, where you would be more likely to see the fall of shot, rather than the rounds sailing over the heads of your enemy, leaving you nothing but a hole in thin air to not see.