Adam my dear friend it's quite simple really. You see in target shooting in the UK and the Old Commonwealth the Enfield action re-barreled to 7.62 Nato using a heavy hammer forged barrel like the Envoy, Enforcer and the L42 rifles were until a few years ago still very popular in main stream target shooting and used in the annual Bisley Imperial meeting and of course in places like Australia and New Zealand.
Instead of working within the design paprameters of the Enfield action these experts using the New Sierra 155 Grain Palma Match Bullet proceded to load them up to a velocity which would maintain a supersonic velocity at 1200 yards as that was the longest distance they competed over and as the bullets slow down and come back through the sound barrier they of course get severly buffeted which of course effects their performance of grouping on the target. Now instead of laying the blame squarely where it lies at the feet of these idiots who overloaded and in doing so vastly over pressured/overstressed the action, instead they those who control the target shooting in New Zealand knowing as they do just how EXPERT their target shooters are blaimed the rifle and banned it's use. This of course caused some trouble as at that time a British rifle team was about to travel to NZ for a competition and some members of that team were of course using Envoy rifles which is built on an Enfield No4 action.
Our NRA based at Bisley Camp is now trying to insist that all 7.62 Nato convert Lee Enfields be re-proofed at 20 tons. It seems that the "target" shooters cannot be wrong it MUST be the action despite the fact that the Army and Police and hundreds of sensible shooters have been using converted Enfields since the mid 1950's without problems until this little episode with the then new Palma match Bullet. Oh btw the proof pressure for the .270 Win is 19 Tons
I cannot think of anyone who in their right mind would consider the Enfield action capable of routinely handling the same pressure as that of the .300 Win Mag
In the Imperial meeting pressures are not a problem as normal Nato target grade ammunition is issued to each competitor. It's in the free matches which allows the use of Handloaded ammunition which cause the problem
Bear in mind that the Enfield was designed with a pressure for service ammunition of around 45,000 and not the 52,000 of the .308 Winchester let alone the pressures that a hot load in the .308 case can reach.