Was the 144gn Ball ammo "disallowed" or was this an intended result of Jackboot Johnny nullifying the defence Act (1910?), eliminating the legislated role of the "rifle clubs” as a official "arm" of the "reserve" services?
The "rifle clubs” brought this on themselves when back in 1959 / 60, they got their noses out of joint and declared the L1A1 "unsuitable and not adaptable to target shooting”.
They had previously got all bitter and twisted over the adoption of the Rifle No1 (SMLE) as the "service" rifle, bemoaning its alleged "Unsuitability" due o lower muzzle velocities from a shorter barrel.. There were all manner of strange experiments going on to inctreased muzzle velocity; like progressively lapping the lands to reduce "resistance”, and so on. NONE of them could perform as consistently as the mass-produced MF Mk 7 ball ammo, however.
As someone who turned several L1A1s into "race-guns” by applying mechanical principals, selective fitting and quality barrels (standard profile, but made using Schultz and Larsen or other high-quality blanks.
It was a bit like backing up the work of the US Army Marksmanship Unit, who turned the "sow's ear" of the "rattly old" M-14 into a fabulous "match rifle" and into the XM-21 and M-25 sniper rigs, still floating around "interesting places”, nearly fifty years later. I did several here in Oz, before the sky fell in; 6 inches groups at 500 yds. was "acceptance"; using "issue" (often "Hythe")sights.
Add to that, things like Incredibly high-quality bullets like Lapua Scenars and "Palma" brass that uses Small Rifle Magnum primers and some seriously "magic" propellants, and it is a whole different game. Precision flash-hole reaming and chamfering? Check. Consistent neck-reaming / sizing. MINIMIZE the feral "variables";ONE at a TIME..
One microscopic "burr" on the lands at the muzzle can "ruin" a barrel, relatively speaking.
It is al a LONG way from the sort of performances that wowed the world of rifle shooting 125 years ago.. So; Less "Voodoo" and more actual "Engineering" seems to be the way to go.
Oddly, enough, good engineering and attention to detain trump "Fudd-Lore" EVERY TIME.