Having gone through the range shooting game at the time of H barreled Mk111s, 2,4 + grooved No4s the 7.62 conversion a heavy barrel, the lack of 303 ammo was the deciding factor. We were not allowed to reload then. Why did the Brits refuse to let the Aussies use H barrels at Bisley. They were Australianarmy issue.
The H barrel is a standard Long Lee shorten to SMLE length and the muzzle turned down to take the SMLE fore sight.