Interesting

[Bruce_in_Oz]

Note the aluminium inner "cap", in both the "experimenta"l bullet and in ALL Mk 7 bullets.

Somewhere along the line, it was decided to make the overall bullet length similar to the Mk 6.

It was also a mechanical requirement to have an overall cartridge length VERY similar (and no longer than) Mk 6, otherwise a LOT of small arms, particularly machine guns and most importantly maxim and Vickers Belt-fed types, would r4equire re-engineering of their feed system components.

By designing a "spitzer" bullet, a lot of weight went away, nut not quite enough, Hence the internal lightweight "cap". The boffins had settle on the concept of a high-velocity bullet and a spitzer shape was a good start. Shaving a bit more weight of would get the muzzle velocity and hence trajectory they also wanted.Because the Mk 7 retained the length, the RIFLING twist of 1:10 inches was, conveniently "a good thing".

That the bullet was "base-heavy" and thus destabilized on transition from air to more "wet" targets, the "body-counters" were probably overjoyed that terminal results were suitably gruesome even though the bullet met all the conditions of the Hague Convention. While forward "velocity is shed rapidly in flight, the ROTATIONAL rate of a bullet barely changes after leaving the muzzle., so, being struck by a Mk 7 bullet, at extreme MG ranges, and thus subsonic, will DEFINITELY 'leave a mark".

Interestingly, Mk 8 bullets do NOT have that lightweight inner cap, but they have a reasonable "boat-tail" Hence a weight of 180 gn, and the boat-tail contributed to less dispersion at trans-sonic and subsonic speeds. . Derived from pre-WW2r experiments with bullets for long-range target shooting.