If I remember correctly the 2A is made from Chrome Vanadium steel.
Addition of Vanadium is more for superior machining properties than for strength though it is stronger than carbon steels.
Experiments in rebarreling Lithgow Nickel Steel No.1 receivers to 7.62 NATO resulted in cracks at the holes drilled for mounting the charger bridge, and some stretching, I don't think any other early Enfield receivers were modified except of course the No.4 rifles in limited quantity.
The British NATO loading is comparatively mild, though not as light as the Spanish loads.

Take care when choosing 7.62 NATO ammo.
I was given several dozen rounds of South American 7.62 with corroded casings to break down for the powder. The powder was a Geman style flake powder.
It smelled a bit strong and some of months later on when I opened the drawer in which I'd stored the steel can containing the salvaged powder I found the can had disintegrated into a fine dusty rust and all steel objects in the drawer were heavily rusted. The powder must have broken down releasing a corrosive vapor.
The bullets also lost their gilding metal exposing the steel jacket.
Glad I never got around to trying that powder in reloads.

When the Spanish 7.62 Mausers first showed up in quantity a number of these blew out when using ammo that should have been loaded to safe pressures.
The problem was not the rifles themselves, though not the strongest actions, but rather defective ammo.
Some of the ammo gave pressures of 68,000 PSI with some going past 70,000.
The theory was these were proof loads accidentally mixed in with service ammo. If I remember correctly these were stamped as "Santa Barbra".

I haven't heard any similar horror stories involving the Indian 2A rifles, they seem to be well made and of very strong alloys.

I just remembered a detail of the metalurgy of the Lithgow rifles that failed to hold up to 7.62 pressures, probably proof loads rather than service loads. The Lithgow rifles were made from a Colt alloy of high Nickel content steel. The best ores available in Australia at the time contained a higher than normal nickel content so they chose the Colt patented alloy to take advantage of that. The early Australian Enfields were actually made at the Colt factory until machinery supplied by Colt was delivered.
The only Colt alloy I remember as being in advance of those used by other gun makers was "Colt Silver Spring Steel". This was an early form of high strength Steel alloy (possibly a Manganese alloy)concocted by a gunsmith to cut down on spring breakage. Colt chose this alloy for his revolvers after the disasterous chamber fractures of the early Colt Walker revolvers. As far as I know all subsequent Colt BP revolvers were made from this steel.
I know that my Older Brother's original Colt 1851 , found buried near a battlefield after around a century, has a main spring stronger and snappier than that of my modern replica.
Lebels were manufactured using Winchester Fluid Steel, another proprietary Molybdenum alloy.

Now bear with me a moment.

My theory is that the strength of the alloy was not what caused the Lithgow failures, at least not by itself.
I've often thought that the method of mounting the Charger bridge was not that well thought out. The threaded holes are a bit too large and too close together.
Since the rifles converted for testing were late WW 2 manufacture its not unlikely that quality control may have begun to slip, especially in the heat treatment.

I've only handled a 2A once but it seemed to me that the receiver seemed beefier.
Has anyone checked on the placement of the charger bridge screws?
If so are they in the same locations as were those of the earlier No.1 actions?

The No.4 receiver left sidewall is a good deal more robust than that of the No.1, but the No.4 Bolt is if anything less robust. The no.4 seems to work fine converted to 7.62. Perhaps because there are no holes in the sides for mounting the bridge.

Hmmm and I thought that the Lithgow machinery came from Britain

Probably so in later years. Or more likely Australian manufactured machinery replaced earlier imported machines as time went on.
The Colt manufactured Lithgows are very rare.

Since the Lee rifles were in use by the US Navy long before J P Lee offered his design to the British, American manufacturers were very familar with the design and the method of manufacture.

PS

4.4 The American System Abroad

Robbins and Lawrence, a machine tool builder that had perfected the use of the American System, seeing the commercial potential of their work, exhibited their guns at the Crystal Palace Industrial Exposition in 1851, where the rifles garnered an award and attracted such attention that Parliament was induced to send a commission to the United States to study "the American system" of interchangeable manufacture and secure the machinery necessary to introduce it at the Enfield Armory near London. The company received an immediate order for 20,000 Enfield rifles with interchangeable parts and 157 metal working machines to equip the armory at Enfield. [Roe1926, p 138] With this order, Robbins and Lawrence became the first large-scale exporter of machine tools.

When Samuel Colt set up his own integrated factory near London, the American System was placed on display and soon held in awe by all the major arsenals in Europe. Pratt and Whitney, one of the major machine tool builders that supplied the Colt factory, was soon receiving orders from almost every country in Europe for machinery (see Figure 4.5, "Milling machines for gun-making, circa 1885; note multiple pulleys to adjust speeds [Hutton1885, p 142]") with which to set up factories.

So the Colt Machinery may have been manufactured by other US companies. The Colt made Lithgow rifles were likely only a test run of the machinery and manufacturing methods. The Colt high nickel steel alloy may have required different settings and other fine tuning of the machinery. Lithgow machinists were probably trained by Colt supervisors, either in Hartford or later in Australia.

I'm sure that the gauges and such were supplied by Enfield along with trained personel to get the operation up and running.

Apparently Enfield had been using american supplied machinery since the mid 19th century, starting with the Ames stock making machinery used for Enfield rifled muskets.

As Patent protections lapsed the machinery could be manufactured by other sources closer to home.

Colt had a long , and highly productive for both parties, association with Enfield.

Whitworth "Fluid Compressed Steel" was for castings , the Colt Silver Spring Steel was for drop forged and machined components.
I don't think the Enfield used any castings. The Colt frames may have been cast but the frames never gave any problems, it was the cylinder walls of the Walker which sometimes cracked and they were not castings.

PS
I said Molybdenum earlier, I think it was Manganese.
I'll try to find out exactly what the composition was.

Well I've found this so far.

Silver steel or high-carbon bright steel gets its name from its appearance. It is a very-high carbon steel. It is defined under the steel specification standards BS-1407. It is a 1%-carbon tool steel which can be ground to close tolerances. Usually the range of carbon is in the range 1.10% - 1.20%. It also contains trace elements of 0.35% Mn (range 0.30-0.40%), 0.40% Cr (range 0.4-0.5%), 0.30% Si (range 0.1-0.3%), and also sometimes sulfur (max 0.035%) and phosphorus (max 0.035%). Silver steel is sometimes used for making straight razors, due to its ability to produce and hold a micro-fine edge.

So the Manganese was present as a mere trace element though it probably added something to the alloy's total strength.
True Manganese steels weren't invented till the 1880's.

Well from a treatise on Nickel Steels I just started reading the addition of Nickel greatly strengthens any Steel alloy and even more greatly increases its "Elastic Strength" a very usful property in a rifle receiver especially the Enfield receiver with its known tendency to stretch and spring back into shape due to its rear locking lugs.
To get back to my theory I can only conclude that the unfortunate positioning of the threaded holes for the Charger bridge is the reason the converted Lithgow rifles did not hold up to the 7.62 NATO pressures, which really aren't much greater than the max pressures of late WW2 Mark 8Z loads.

I'll try to find out more about the 2A Vanadium steel alloys next.

The original Lee Mk1 Rifle was designed to handle the 303 cartridge and it's associated service pressures which is did perfectly well. Much is made, usually by Americans funnily enough, about the rear locking action. I have even heard people claim it only has one lug however several commercial rifles have been made in the recent past and may still be in production that use rear locking lugs. Did not the Rem 788 have this feature? yet is was highly thought of for it's accuracy. Heym also makes/made a rifle with rear locking lugs yet I have never heard that it was weak and Mauser also made a mode with rear locking lugs.

Well Kevin first off, surely you've noticed the offset of the No.1 front sight base.
This offset is there because the rear lockup combined with the necessarily open righthand side of the action , to allow loading and ejection, results in unequal support of the bolt body and the near microscopic springing of the receiver rail that "throws" the bullet. The receiver effectively adds a wild card to the other factors of barrel harmonics.

The Mark 8z was not intended for use in rifles but shortages resulted in it being issued late in the war. It was found that rifles with new or unworn rifling handled the round well but rifles with any wear to the throat from the higher temperatures of Cordite ,while still accurate with Mk7 loads, would keyhole Mk8z rounds.

The No.4 lockup is not much if any stronger than the No.1 lockup but the thick high lefthand sidewall of the no.4 stiffens the receiver, and the heavier barrel of later versions, especially the Savage and Longbranch rifles,
Added to that virtually eliminated the Bullet "throw".
An accidental discovery due to a wartime shortcut revealed that barrels not finished turned beyond two inches ahead of the knox form were most accurate. The skipping of that step in the turning process left the barrel thicker at that point than immediately behind that point. This created a dampening effect that further offset the effects of barrel vibrations and isolated the barrel from the harmonics of the receiver.

You might have noticed that I prefer the No.4 Enfield action to mauser types, mainly for its ergonomics. I respect it for its strengths and work around its weaknesses.

James Paris Lee, who originated the action type, designed an improved four lug lockup for a military rifle in 7mm Mauser caliber. This is a very rare rifle, if indeed any still exist. The improved lee action used the standard rear lugs coupled with a forward locking pair of lugs and a Manlicher type bolthead.
I've only seen cutaway drawings of the action and catalog drawings of the rifle which greatly resembled the Lee Metford rifles.
This would have made for a fine rifle, more suitable for the following generations of smokeless propellents.

Cordite has a number of excellent qualities, and gives good velocities at much lower pressures than other smokeless propellents, but at the price of greatly increased operating temperatures.

Did not the Rem 788 have this feature? yet is was highly thought of for it's accuracy. Heym also makes/made a rifle with rear locking lugs yet I have never heard that it was weak and Mauser also made a mode with rear locking lugs.

I used to own a 788 in .243 Winchester. A fine rifle in its way , but limited in the types of ammo it could digest. It was not as successful as you might think. The rear locking lugs had less effect on accuracy due to the very heavy cylindrical receiver body. Cutouts for the ejector port and magazine opening were much smaller than those of the Enfield. Metalurgy was also slightly superior to run of the mill Enfields, though there are reports of the actions not holding up well to extended firing of hot loads.
The 788 was never considered to be suitable for truly high intensity cartridges, though it handled the .308 well enough as long as factory pressures were not exceeded.
I'm not familar with the Mauser design you speak of.

I mentioned that I prefer the Enfield for its ergonomics. Due to injuries to my right hand I have some difficulty operating the mauser style bolts and the enfield's short bolt throw is another plus. You may remember that I also use a Savage 23B which also has the rear lockup and short bolt throw.
In fact every rifle and bolt shotgun I own has a rear locking action and short throw.

My interest in this thread is just why the 2A can handle the 7.62 NATO when the Lithgow can not, I don't think its a matter of the Vanadium steel alone.

One thing you should consider is that a beneficial property of Vanadium alloy is that it makes manufacturing easier, theres less chance of one receiver being less strong than another of the same run. There are fewer rejects and fewer suprizes down the road.

Since the failure point of the lithgow test rifles is known, theres a possibility that the vanadium alloy made the drilling and tapping of the charger bridge holes somehow less destructive of the receivers integrity.
Theres a fair amount of metal removed to counter sink the sides of the charge bridge into the receiver wall and rail. This may also have been a factor.

As for whitworth steel. He made a leap forwards in steel production , but a treaise of the day says that Whitworth compressed Fluid steel had already been replaced in US industry by Bethlehem Fluid steels.
Every genius stands on the shoulders of Giants.
Whitworth created principles that allowed the industry to further advance precision mass production but Pratt and Whitney did the necessary work to put his discoveries to use in the real world.
Colt recognized genius and put that genius to work.

but the US wanted Britian to adopt THEIR RIFLES AND CARTRIDGE of inferior design so the the US could make more money and control supply.

Think for a moment.
Did Britain ever adopt the M14 rifle?
Did Britain produce its own 7.62 NATO ammo for its Belgian designed FN FAL rifles.
Wasn't the Bren Gun easily converted to 7.62 NATO?

Far too many swear by the 7.62 and its combat effectiveness to consider it an inferior cartridge.

Isn't the Bullpup Enfield rifle roundly despised by those who use it, and not for its cartridge but for the very design features it shares with the EM2?

I do agree than the British .280 was a better assault rifle round than the 5.56, and modern developments of the 6.8 Remington would seem to indicate that US weapons designers would agree.
Ballistically both are very close to the .276 Pederson originally planned for the US Garand (designed by a Canadian BTW).

I have a friend who was involved in the troop trials of the 280 and EM2 and some years ago I met the person who loaded the development cartridges during it's development and testing so learned first hand of this and what happened at that time.

I'd like to hear more about the development of the .280. Especially if they have any info on the test bed rifles built on the No.5 action.


PS

In 1909 Pratt & Whitney secured a contract for the

Australian Arsenal at Lithgow, Australia. Bids were called for

in London, for a plant having a production capacity of fifty

Lee-Enfield rifles per day. When Pratt & Whitney Company

sought permission to bid, it was thought impossible to build

the plant outside of England, as there would be no access

to British Gages, and the Australian and British gun parts must

interchange.

Pratt & Whitney Company declared they could produce

a plant to duplicate the British weapon by using the interchangeable

system of manufacturing. The best English bid and the

Pratt & Whitney bid were almost identical, but the English firm

required 700 machines to do the work against the Pratt &

Whitney estimate of 300.

The question of working hours to produce a gun also came

up, and Pratt & Whitney Company guaranteed twenty-three

hours per gun against the English seventy-two hours.

Commander Clarkson was sent to the United States to

investigate, and the contract was awarded to Pratt & Whitney

Company, as he found their equipment far in advance of anything

he had seen previously. The machinery was tested before

shipment from the United States and the time per gun actually

was lessened. Experts from Hartford were sent to Australia to

set up the plant and train the operators. In 1912 the plant was

in full operation, and one of the Hartford men was retained as

manager of it.

http://www.prattandwhitney.com/history.htm
Page 45

I guess Pratt&Whitney and Colt colaborated on this venture, both based in Hartford Conneticut.