Looking into the pressure levels of various recommended loadings of the .308 you'll find that pressure levels increase greatly as heavier and longer bullets are used. Many loadings that come near to duplicating the most common Britishicon military loads for 7.62 NATO are very close in pressure levels to the .303, but others that employ heavier bullets far exceed those pressure levels.

The .308 has a short neck and overall length was always a major factor of the design. The heavier and longer bullets extend into the case and take up space reducing effective case capacity. When the arm is magazine fed you can't increase OAL so the reduction in capacity is something you can't get around so long as bullets of conventional construction are used.
The majority of Infantry rifle 7.62 uses bullets of less than 150 grains and seats aproximately even with the bottom of the neck leaving the case capacity at is greatest, while bullets heavier than 150 can extend into the case reducing effective capacity.
Match loadings of the 7.62 are generally 169-175 grain projectiles loaded to only 200 FPS higher than the .303 MkVII of the same bullet weight, with pressures only a bit in excess of maximum safe levels for the .303, but some .308 sporting ammunition is not intended for game in the same weight class as human beings, the .308 is used for Moose and Bear in this country and top end loads generate pressures greatly in excess of the maximum safe limits for the .303 rifles and 7.62X51 conversions of those rifles, and very likely to levels unsafe for numerous other rifle types converted to 7.62 NATO.

The .303 can of course take Moose and Bear, but the .308 loads for game in this class far exceed the performance of the hottest .303 loads.

Even the mild US Match grade 7.62 exceeds the pressure levels of MkVIIIZ ammunition and the British did not consider it wise to use MkVIIIZ ammunition in the No.4 rifle, and potentially dangerous to use in the SMLE rifles.
An analology would be use of +P .38 special ammunition in a antique .38 special. It might well digest many rounds without obvious damage but the metalurgy was generally not up to such pressures and the top straps were seldom as sturdy. Some revolvers had enough margin for error built in that +p might never cause a problem, and the .38-44 revolvers built on heavier frames were in fact intended for the hottest loads available before the .357 came along.
Ability to digest standard pressure .38 Special ammunition does not mean a revolver can be expected to digest .38 +P, and the ability of one example of a particular revolver to handle +P without obvious damage does not mean that every other revolver of that type can do the same.

I've seen No.4 rifles in good condition fail to extract commonly available .303 freshly manufactured S&B FMJ 180 grain bullet ammunition, the casing swollen and stuck firmly in the chamber. This happened only occasionally, on the hottest days of that summer, with the other cartridges from the same boxes behaving normally. Nothing about the appearance of this ammunition gave any indication that it had degraded in any way. The ammo was most likely well within specifications, but there are always variations in pressure from one round to another with some ammunition varying several thousand pounds. Add to this the effects of heat, it was 99 degrees F here yesterday, and temperatures of 100+ are common in summer. Temperatures of 130+ degrees have been recorded in Iraq in recent years.

I looked up some available information on the L42 in service and found one British sniper quoted as saying his L42 jammed in action so badly that he discarded it and used an FAL instead.
When a Enfield jams its almost certainly a failure to extract, so I suspect the ammunition he was issued was at fault.
The rifle has a great reputation so long as the 144 grain ammunition is used, but not so great when 155 grain bullets or heavier are used. Its unlikely that more recent heavy bullet long range 7.62 Ammunition would work reliably in the L42, so thats probably why that rifle jammed.


If a No.4 converted to 7.62 were used with the hottest heavy bullet Moose and Bear loads which even milder reloading manuals list at 59,000+ PSI then it would be subjected to pressures near those of proof testing for .303 rifles at every shot. No rifle is expected to handle proof test ammo for more than a very few shots without damage, and British Proof laws do make allowances for rifles damaged during proof to be repaired and re submitted.



Now as for the SMLE's reputation for withstanding the mud of the trenches. If you study the book I linked to early on in this thread , and Reynolds "Lee Enfield" you'll find that theres no claim that it was safe to fire muddy cartridges, only that should the action become muddied it was far easier to remove the bolt and clean out the mud than with some other designs. The split bridge and short bearing surfaces of the rear receiver, plus all the open spaces under it gave mud a place to go where it wouldn't interfere with functioning of the action. A tiny amount of grit clinging to a cartridge case after a swift wiping off would not prevent chambering.
Firing a dirty or muddy cartridge in an Enfield was certainly no safer than it would have been in much stronger actions.
Firing a cartridge simply wet by rain could cause excessive pressures a great shift in POI and possible fracturing of the receiver. I've never heard of a wet cartridge fracturing a Mauser or Springfield receiver. That might happen with a thick coating of grease but not likely that a little rain would destroy either of those rifles even at their much higher operating pressures.

The ability of the SMLE to continue operating under rough conditions depended more on its open design and easily removable magazine. The magazine if clogged with mudd from reloading with muddy hands, could be rapidly removed and if necessary replaced with a clean one salvaged from a battlefield pick up.
The orignal Lee design had called for spare magazines to be carried in bandoleers. Charger loading made it cheaper to issue only one magazine, so the only advantage of the quick detachable box magazine was rapid replacement if necessary, and ease of cleaning.

The Enfield bolt can not be rapidly field stripped without tools, in this respect it was inferior to the Mauser.

I've seen nothing that indicates that jamming or failure to extract was at all a problem with the Mauser or the Springfield under the conditions of the trenches. Some other contemporary European rifles may not have faired so well.

It would appear that as far as functioning is concerned the Enfield was not remarkably better than the Springfield or Mausers.
It was not as strong and in general less accurate with shorter effective range.
While the Windage adjustable rear sight was superior to the sights of contemporary rifles, that feature was dispensed with by the MkIII* as a production shortcut, so Wartime production SMLE rifles did not benefit from earlier superiority of the sights.

The ten round capacity was the Enfields greatest advantage, and while I've found that the Kragicon was every bit as fast to operate, the Krag was already obsolete and saw almost no combat during WW2.
So capacity and speed of operation are solidly on the side of the Enfield when WW1 battle rifles are compared.
Power, penetration, range, and accuracy are solidly on the side of the Mauser and Springfield.
Durability of the stocks seems to have varied greatly with the SMLE, with Hesketh-Pritchard saying warped fore ends were very common in the trenches.
Whether Mauser or Springfield stocks had problems of warping is impossible to say, but changes in bedding caused far less accuracy problems for those rifles.

Before WW1 the British had already begun to look for a replacement for the SMLE, the first experiments were actually done with US Springfield rifles, so while there are elements of the Mauser design in the Springfield those same elements were carried over into the P-14 from the Springfield.

The P-14 was considered superior to the Scoped SMLE rifles for sniping, and even sporting rifles had to be pressed into service to make up for the SMLE's shart comings in both long range accuracy and lack of penetration of the service ammunition.

Testing of WW1 era body armor and sniper shields showed that MkVII ammunition was the least effective of any service ammunition against even those primitive breastplates and shields.

The No.4 rifles are marginally stronger but that has no effect on the strength of the SMLE rifles, and comparasions to the P-14 show that the improvements of the No.4 did not completely eliminate the shortcomings of the rear locking action and split bridge receiver.

The complaints of the "Unscientific Bolt" and weaknesses of the SMLE came from British and Canadianicon sources, not from any mythical "American Gunsmith". Though no doubt at least some have repeated the well founded criticisms of the Enfield.


Besides racks full of badly abused Enfields on sale here in the 80's I well remember the trash cans full of badly damaged Enfields that were to be found at discount stores, priced at a few dollars each to be used as decorator items or stripped for spare parts.
Millions of Enfields were produced, and hundreds of thousands if not millions are probably still around in good condition, but millions were also worn out or damaged by use with unsuitable ammunition.

I've had to repeat myself alot here because some don't seem to get the point.
I don't have a mountain of images that I can post with misleading and spurious claims or cherry picked manual entries to misrepresent either.