Thread: "Metalurgy" Notes
Retrieved: 06/05/2014

I have not yet seen any original documents that precisely describe the process(es) of heat-treating the bolt body of any Lee Enfield.

There would have been several such processes, as all four bearing surfaces of the lugs should have been sufficiently hard to minimise wear, but not to be brittle.

The main "body" of the lugs should have been "tough" to support this hardened skin and , particularly, to have some elasticity to cope with the forces transmitted during the shock of firing.

If this process were not done correctly, especially in the days before pyrometers etc, and given that, to the end, SMLES were made from various grades of CARBON steel, (NO "fancy alloys" allowed except under very special circumstances), the potential for "over-cooking" the metal was very much present.

The bolt body started out as a straight bar of steel and was FORGED into an "L" shape before being machined to final form. The forming of the long "tail" on earlier LE bolts must have been REAL fun!

The 1903 Spec (S.A. 242 (1903)) for the Mk1 SMLE states that the bolt body was made from "56A42 Crucible steel, oil-hardened, tempered and browned".56A42 is actually a low-carbon (0.67 to 0.77") steel and the stuff used in the bolts was to have vanishingly small traces of Manganese, Phosphorus, Sulphur and Silicon.

The 1938 Spec (S.A. 462P) specifies "D.D.8" steel, oil-hardened, tempered, polished and browned (blued" or oil-blacked.Both recipes seem to rely on selected Swedish ore for the base material. One source of problems is in the coal used to produce the coke in the furnace. Some coal contains significant traces of Phosphorus and Sulphur, neither of which are desirable.

Interestingly, at some, as yet unknown date, Lithgow started using what I suspect was "electric" heating for the heat-treating of the locking shoulders in the body. If you are lucky enough to have a "MINT" Lithgow SMLE (usually WW2 or later), or one of the WW2 XP carbines, take a close look at the exterior of the left and right sides, just behind the locking shoulders.

There you should find a small circle of discolouration and surface distortion, a bit like tiny "spot-welding" scars. I understand that these marks were left by the application of Carbon electrodes that delivered the current to "spot" heat the metal before quenching.

Thus, the remainder of the body would be in a "toughened" (strong, but NOT brittle) condition, and thus able to withstand the "shock load" of firing.

Later "FTR" activity seems to erase these little heat-treatment marks.

jmoore
09-30-2013

Originally Posted by Bruce_in_Oz
The 1903 Spec (S.A. 242 (1903)) for the Mk1 SMLE states that the bolt body was made from "56A42 Crucible steel, oil-hardened, tempered and browned".56A42 is actually a low-carbon (0.67 to 0.77") steel and the stuff used in the bolts was to have vanishingly small traces of Manganese, Phosphorus, Sulphur and Silicon.

I'm guessing that 0.67 to 0.77 number is "percent"? Not what I'd call a "low carbon" steel! That much carbon would put it well into the "high carbon" classification. Given the ductile nature of most SMLE receivers, I would have to guess that the heat treatment was somehow localized by slowing the cooling rate away from the locking surfaces. Spot hardening or induction hardening those areas would be later innovations, I'm thinking not generally used before the 1920s, but I am making a SWAG based on examples of such tech seen elsewhere.

Bruce_in_Oz
09-30-2013

Thanks for the reply and corrections.

I guess it is fairly obvious that I am NOT a metalurgist; just an enthusiast with an enquiring mind.

jmoore
09-30-2013

The reason I asked is that it's not hard to misplace the decimal point if you are not familiar with such things. It's barely conceivable that the numbers were 0.067 to 0.077%, which would be a very low carbon alloy. But highly unlikely! Too close a control, for one thing. And without other strengthening elements it would be way soft and virtually "un heat treatable". 6.7 to 7.7% is right out as well.

Like lots of things, there's specifications within specifications. What would be the next step would be to find is any documentation of the oil quench specs for this alloy, and any processing notes for the receiver. (Partial quench to a certain depth, or clay masking, etc.)

Detroit-1
09-30-2013

Originally Posted by Bruce_in_Oz
Interestingly, at some, as yet unknown date, Lithgow started using what I suspect was "electric" heating for the heat-treating of the locking shoulders in the body. If you are lucky enough to have a "MINT" Lithgow SMLE (usually WW2 or later), or one of the WW2 XP carbines, take a close look at the exterior of the left and right sides, just behind the locking shoulders.

There you should find a small circle of discolouration and surface distortion, a bit like tiny "spot-welding" scars. I understand that these marks were left by the application of Carbon electrodes that delivered the current to "spot" heat the metal before quenching.

I have a all matching non FTR'ed 1945 Lithgow that on the left side behind the charging bridge is the circle that you are talking about.

303Guy
09-30-2013

My 1944 Lithgow has them. They look like punch marks with a 'disturbance' around them. Mine is a Sportco 25/303. Thanks for the information. I would like confirmation on the steels used in later Lee Enfields including the No4. I've been told that the American built No4's used a stronger alloy than the British and these alledgedly withstood 7.62 NATO proof loads better than the Brit made ones.

Peter Laidler
10-01-2013

Your last sentence is yet another myth 303guy. What we in REME circles call 'a load of old boll-...' I'm struggling to find the word I'm looking for again! They were all made to a strict criteria, made to our spec, for us! And if any of your old shooting friends tell you that the Indian 7.62's were also made from a tougher steel, then tell them that that is also a load of old whatsit too.

Can any of you less refined forumers help me find these words that keep slipping from my memory banks. Maybe my lingustic skills are fading now that I have left an Infantry/REME workshop environment

muffett.2008
10-01-2013

Back to Bruce's original, in my files I have the Lithgow SAF requirements for all metals, but this is the one you are interested in.

Just ask if you want the rest.

bigduke6
10-01-2013

As were on the subject (not regarding old posts etc) but regarding Metals, I've just ordered the book below in the link, more of an interest thing but may help when I start studying again (my old notes from my apprenticeship I cant read or decipher) just wonder if anyone has it on their bookshelf ?

Handbook of Metal Treatments and Testing: Amazon.co.uk: R.B. Ross: Books

Peter Laidler
10-01-2013

If you really start on the metallurgy trail, be ready for the looooooong haul, believe me! Even the Mech Eng Uni courses 'do' the subject, in real terms, as you learn when you're out in the real big bad world, it's no more than glossing over. In fact it's a degree in its own right

On the down side, I find that while many of them soon become PHd's/Doctors, they get a bit nerdish/blinkered. Only my take on things

bigduke6
10-01-2013

On the down side, I find that while many of them soon become PHd's/Doctors, they get a bit nerdish/blinkered. Only my take on things

No its not a start on the Metallurgy trail, in my job our Certificates are never deemed to match or are equal to anything shore based although we study the same subjects such as Maths, Applied Mechanics, Heat etc, and only some shore based Companies recognize Merchant Navy Qualifications, so thought I,d look at a degree with the Open University.

I'll be sticking to Engineering (may have an advantage with this) this would give me an exemption for My Cheif Engineers (part A) and provide with me with more points such as the 15 I,m short of, for NZ and automatic selection.

I think I mentioned it before but looked at it a while back and sent off all my qualifications I had, to see if I could get a few credits, must admit after serving a 4 year apprenticeship (a proper one), 23 years at sea with qualifications in the subjects above, being Corgi Registered (now Gas Safe), several heating qualifications and a few shooting medals I thought I may get a few, they come back with my credits, Dear Mr. ...your credits for the above...

What got my back up at the time if I went to one of the many evening Lectures available for adult learning (all subjects), I could get around 2 credits for each one.

So thought about the old saying "If you can't beat them, join them."

lee_enfield223
10-03-2013

I have read in two books (one by Skennerton) that the Indian 2A1 (7.62) receivers were made from EN36A steel! Not trying to say Peter is wrong in anyway (but have we all been misinformed?) Anyway I have machined up lots of parts for machinery using this steel and had it case hardened, (I used to work for 23 years in one of the largest automotive plants in the southern hemisphere as a toolmaker) and found this steel was also used the in the Australian automatic arms SAR which went into the rifle trials against the styer aug F88 the manufacturer used EN36A steel case hardened to a depth of 0.010" at 56 to 59 Rockwell hardness (how do I know what they used? Well I rang the guy who made the AAA rifles)

Please feel free to comment as I would like to see these books proved wrong, and if so I'll be selling my 2A1.

Peter Laidler
10-03-2013

The first test is simple. Just look at some of them and guess what... They are based on old converted No1 rifle bodies! Another is that if the old No1 in .303" is proofed at 18.5 tons and the 7.62 at 19 tons... (I know it not quite that simple in this respect but it does illustrate the point) and 3... do you want me to go on?

Bruce_in_Oz
10-03-2013

"the old No1 in .303" is proofed at 18.5 tons and the 7.62 at 19 tons..."

Here's another thing:

Has anyone looked at the throating of a 2A1?

If the barrel is throated like a bench-rest rifle, with the ogive of the bullet touching or actually engaged in the lands, you can expect a fairly "sharp" pressure-curve rise time and high "peak" pressure. You can also expect VERY consistent propellant combustion and thus muzzle velocities.

IF the barrel is throated with a bit of "free-bore", then the PEAK pressure will be lower and the "dwell-time" of that lower pressure will be a bit longer than otherwise. The free-bore allows the bullet to start to move virtually as the primer ignites and before the main propellant has really got going.

Early (and "easy") movement of the bullet effectively increased the volume in which the main charge starts its burn. More volume means less starting pressure and a lower peak pressure. NC powders burn faster the more they are contained, so, a bit of "extra space" effectively slows down the initial burn rate.

It's a bit like the difference between being whacked with ball-pein hammer vs. a rubber mallet.

Has anyone with a "mint" 2A1 ever tried to do a casting of the chamber and leade/throat of the barrel?

So, given the rather rapid burn rate of good-old Cordite, a bit of freebore may not be a bad thing in a .303 chambering. With the larger quantity of slower-burning, granulated nitrocellulose propellants in the 7.62 NATO cartridge in a SMLE action, some freebore would be a fairly good precaution.

lee_enfield223
10-03-2013

Hmmm I have never seen one built on a 303 action body, but it does not surprise me in the least, I had a real good look at mine and it does appear to have a new 2a1 action, also the cut out for the magazine in the action is of a different shape to my Lithgow 303, getting back to throats, lots of surplus rifles have deep throats, and you are probably correct as I have tested lots of loads in military chambers and found that you can load more powder into a rifle with a long throat.

303Guy
10-03-2013

Your last sentence is yet another myth 303guy.

Thank you Peter, that's all I was looking for!

muffett.2008, may I enquire the date of that document, please?

Peter Laidler
10-04-2013

Back to metallurgists again... I'm not having a go at them (?) as a profession - but in my dealings with them, most recently during a xxxx-xxx trial you always got the impression that if something was built DOWN to a price as opposed to built UP to a spec for maintainability, then they'd be responsible. Just my take on things.

I remember saying about a piece of fabricated crap that it was beyond any sort of repair. In fact beyond any salvation. One of them just commented that '...Peter, it's got an xx life. Bin it and get another at that price' But in the meantime the XXXX-XXX was out of action awaiting another feed shute. Metallurgists

muffett.2008
0-04-2013

1921, I have the 1914 one also, they vary a bit in specs required.

Bruce_in_Oz
10-04-2013

Wait! There's more.

From the 1938 Specs. for the SMLE:

Regarding barrel proof, refer to page 12:

(g) Proof. - The barrel will be submitted with the action attached for proof. The distance from end of bolt to face of barrel will be tested with a cartridge head gauge .067-inch. The proof will then be carried out with a proof cartridge, the charge being about 33 grains of No.3 cordite, having a service bullet of 215 grains, giving a mean pressure not below 24 tons per square inch, after which the action will be examined; and the barrel, body, and bolt head will be marked with the proof mark.

Note:

Composition of the B.S.S.5005/401 steel used in the body (receiver):

Iron (unsurprisingly)
Nickel 2.75 to 3.50 %
Manganese 0.35 to 0.75%
Chrome 0.30%
Carbon 0.25 to 0.35%

So, the SMLE was FACTORY proofed to at least 24 TONS per square inch.

Did Ishapore have a different recipe at the time and did they change it for the 2A1?

lee_enfield223
10-05-2013

Just an observation I have seen two No4 303 actions in the last 7 or 8 years that have been proof tested for the 7.62 at Lithgow, that were fired with the NSWRA winnchester 308 match load(correct me if I am wrong reg the load)about 46grs of 2208 behind a 155gr sierra,and both developed excessive headspace and the locking lug recess bulged into the bolt raceway, so I guess if a No4 can't take it then I would be worried using that ammo in an indian 2A1 !!!! anyway it's just a thought, but I have also seen those number 4 7.62's fire thousands of proper ex mil 7.62 ammo with no hassles.

Peter Laidler
10-05-2013

On the other hand, while you have seen two No4's that can't take it, as a bit part Armourer of the era I've seen a thousand L42's successfully firing 7.62mm. There will probably be a similar amount of No1 conversion's in Idian service that use 7.62mm NATO spec still using it.

I think that you're scaremongering a bit... Just my thoughts for what they're worth.

I only ever saw two catastrophic failures with No4's in my service. In fact, I didn't actrually SEE them, but saw the results of the Board of Enquiry findings. None of which were rifle failures as such but user error. Loads of broked parts etc etc but major failures, just two.