Mk 4 .303 Headstamp Question

[Bruce_in_Oz]

And the prize for the most elegant "work-around" must go to the .303Mk7 projectile.

With higher velocity by a fair margin, than any previous .303 Service bullet and a carefully crafted core inside a much thinner and softer jacket than the older Mk6 cupro nickel job, the Mk7 was very well balanced in flight, but became spectacularly unstable on impact with some unfortunate living tissue.

It is entirely likely that this "jolly" convergence was partly "accidental".

To work in the existing fleet of rifles and MGs, the loaded cartridge had to have the same overall loaded length as the superseded round-nosed jobs. There WAS an experimental "lightweight" bullet doing the "rounds" not long after the Teutonic types introduced their 7.92mm "spitzer" in the early 20th Century. but it was shorter than the final Mk7 and thus was never used in service. That event also stirred the Americans into ditching their "brand-new" .(1903) .30 cal rimless job and introducing the mighty .30-06 and re-jigging a bunch of the equally new Springfield rifles.

A conventional core in this new Mk7 bullet would have meant insufficient weight reduction to achieve the desired velocity and trajectory whilst operating within specified pressures. Hence the little lightweight (paper, aluminium, etc.) filler cone inside the pointy end of the jacket.

This construction gave the required mechanical properties and muzzle velocity. The SMLE, being noticeably shorter than its ancestors, automatically produced lower velocities for any given ammo. Creative "taper-lapping" of the bore to raise muzzle velocity only meant a reduction of both barrel life AND in the precision of shooting.

The other bit of 'serendipity" was that, because the bullet was more-or less the same LENGTH as the old Mk6, the twist-rate in the barrels, as per Greenhill's studies, had to stay the same 1:10" rate. This also allowed the continuing use of earlier pattern ammo for training / "emergencies" as long as one could live with the odd behaviour in the magazines of rifles or the somewhat different range tables for machine-guns.

Moving the centre of mass REARWARDS virtually guaranteed that the bullet, quite stable in flight, would become VERY unstable VERY soon after impact with anything denser than air.