Bear also in mind that 1n 1903, the standard ball ammo was Mk Vl and the experts spent a LOT of effort on weird barrel lapping regimes to try to get the muzzle velocity from the shorter SMLE back up to that of the L. E. rifles.

The advent of Mk Vll ball as a response to the Germanicon development of "S" ball with its lightweight spitzer bullet traveling at not much shy of 2900fps, threw lots of things out of the window. but picked up some bonus points: The Brits tried a "clone", of about 150grains weigh and, with a composite core. It lacked the required long-range performance in machine-guns, so they split the difference and the Mk Vll was born.

In the SMLE, they had a lighter rifle, firing ammo that produced less recoil and bore wear in a shorter barrel. The actual barrel length, 25.2 inches,did not change from the SMLE, through all the trials and into the No4 series, thus the trajectory with Mk Vll ammo was a known commodity. Obviously, the No 5 is shorter, lighter, noisier etc, but it wasn't developed on a wild whim, rather, as a perceived requirement for a rifle that was a bit more suitable for use in "jungles", and for vehicle crews and troops throwing themselves out of aircraft.. Besides all that, the advent of "fire and movement" with a section MG (Lewis, BREN) had altered tactical thinking greatly.