Explain the Original SMLE 303 Headspace Situaiton?

This has come up and I have a curiosity on it regardless not to mention with the 303 Rimmed you wind up like a belted magnum with two different players involved in the chamber as it were (probably not well said but)

Was the purpose of the 4 heads on the latter SMLE to tune to the original manufacturing new gun (tolerance vary that much?)

Of was it a field issue?

I have read the rim thickness variance issues of WWI and if they varied that much, it would been to not matter (at least in combat and a rifle with limited life).

Happy for a good reference, did a lot of searching and came up with nothing on that specific area.

The simple answer of different size bolt heads for the No.4 was production expediency. Select fit for proper headspace and bolt assembly, then send it down the line.

FYI: The No.4 is not an SMLE. That would be the Mk.III/III*.

There has been plenty on here regarding headspace........ so be prepared for a bumpy ride, there is all kinds of crap written here and there, for the .303 the headspace is the thickness of the space between the bolt face & the rear chamber face occupied by the RIM of a loaded case.

Two gauges, NO GO and GO very simple, not sure on the different Bolt heads for the SMLE No1 Mk111.


(Brian, I assume its a SMLE as he refers to WW1)

Post WWI, not sure what date the replaceable bolt heads went into affect

Geoff absolutely said it all. Take his advice and keep it simple. .064 and .074 with a properly fitted bolt assembly are all there is to it.

I guessed RC20 was talking No.4 with the different size bolt heads which were introduced in the 1930's. All part of the No.4 design. Long bolt heads must be hand fitted to spec. on the No.1 SMLE along with all the earlier variants of the Lee Enfield.

perhaps the original poster is asking a question in reference to the "general internet" fact that the multiple number replaceable heads were to be used to deal with head space issues as the rifle was used and the frame stretched out?

Cue dramatic music....

In the beginning....

There were NO manufacturing standards, apart from those set by the makers of "stuff.

This is why ALL British small- arms, military and civil, pre about 1850s used whatever the maker could produce.

Even after people like Whitney and Whitworth got busy, different trades had their own ideas about thread design and specifications.. As an example, the classic BA (British Association) threads are derived from METRIC "Thury" threads as used by Swiss clock-makers. Note that the "Zero" BA (the base of the system), has a thread pitch of ONE millimetre. It then gets weird, as each successive smaller size is 0.9 times the size of the previous thread.

There were, and still are, "Admiralty" threads, used in, as the name suggests, British naval construction. It took a while for the Europeans to sort out their "metric" system(s) AND Britain was the main source of machine-tools at the time, and thus, Mauser used IMPERIAL threads pretty much universally from the beginning and into the 1930s. "Proper" Mauser barrel threads are essentially Whitworth, i.e. 55 degree form and 'threads per inch. See also some of the trigger-guard screws. Type 30 and 38 Arisakas are full of "British" threads, Type 99s are Metric.

Lee Enfields used mostly "Enfield specials. This followed the practice starting with the Pattern 53 and continuing through the Martinis, (a design adapted from a Swiss re-working of an American concept). and continuing up to the No1 MkVi.

At that point, someone noticed that times had changed and so, the No4 series, the "standardized" production version of the Mk6, has "commercial standard" threads, primarily BA and BSF, with the stock bolt carrying on the classic Whitworth that had worked for half a century. There was a very good reason for ditching the old "Enfield specials"; mass, outsourced production of components. Pretty much every mechanical workshop in the country was familiar with BA, Whitworth, BSF etc, especially in the automotive and machine tool biz. The gauging for these "industry-standard" threads was everywhere, as opposed to the near shambles that developed in WW1, trying to outsource mass production of SMLE screws, etc. No certified gauging, no standardized production and no total interchangeability.

How did we get from bolt-heads to screw threads? ALL early production relied on a zillion precision gauges to assess every surface and feature of every component at every phase of manufacture. There was, essentially "ONE" SMLE bolt-head for the life of that rifle in service. They simply relied on the fine tolerances allowed on critical surfaces to "stack" such that with a bit of "hand-fitting of bolt-bodies to bolt-heads to the receiver bodies, it would be within tolerance.

Lithgow DID produce a limited series of "extra" bolt-heads post WW2. This was to keep the old girls going long enough to see in the new L1A1.

The No4 was a bit different; same basic idea, but the "extra" bolt-heads appeared MUCH earlier in the life of the rifle. The SMLE series was made from "straight" carbon steels, carefully heat-treated for hardness, toughness, etc. as requires by the function of the component. It was a bit of a "cottage industry" concept, taken to enormous scales. And we'll skip, whistling, right past the P-14.

The bolt-fitting caper was done by specialist workers at the factories. Trays of carefully-gauged components were selected for "best fit. "Best fit" was VERY tight, because after the complete bolt assembly was fitted to the barreled body, this assembly went to the proofing room where a "different" proof round was fired to "seat" the whole assembly of body, barrel and bolt.

We will also tap-dance past the practice of "taper-lapping" SMLE barrels.....and the differences between the 'Enfield Inch" and the "Pratt and Whitney Inch".

The past is a VERY foreign country at times.

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Originally Posted by Bruce_in_Oz

We will also tap-dance past the practice of "taper-lapping" SMLE barrels....

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No, please don't! Since the usual purpose of a lap is to create an extremely regular surface - whether plane or cylindrical - how on earth does one produce taper lapping?

Yes its quite the good read that book "The Enfield Inch" from my shelves

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Originally Posted by Bruce_in_Oz

after the complete bolt assembly was fitted to the barreled body, this assembly went to the proofing room where a "different" proof round was fired to "seat" the whole assembly of body, barrel and bolt.

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I'd never heard it put that way but it makes sense. The high pressure round would indeed seat things...

Thread 6, Rifle bodies don't stretch.

its a rather "known fact" on certain gunboards such as cast bullets and thefiring line that the enfield receiver stretch over time as its used, claimed to be the reason it could do the mad minute so well, that the receiver stretchs out and over time causes the head space to go bad.

SO that version of rifle was created with replaceable bolt heads so that as the rifle was used and stretched, an armory tech could put a longer one in and get it going again.

Please don't take offense but "known fact"? No offense to gunboards either but I try to look at it from time to time and the crap on there is so overwhelming that i finally gave up.

The bodies don't "stretch", unless subjected to something WAY nastier than tens of thousands of quality ball rounds, but they do WEAR.

If you look at a No1 or No4 body, there is very little bolt support in the vertical. What support there is, comes from heavily cut-away radiused surfaces in the bolt raceway, supporting a mostly round bolt body. It worked for millions of action cycles on millions of rifles. Some wear is inevitable.

Mauser bolts can be a "racing fit" and still manage to pick up a round and chamber it. The design of the SMLE is different, obviously. I am seeing more and more No1 rifles where the bolt-head disengages from the body, about halfway forward. Worn bolt-head, worn guide rail, worn raceway. Sometimes, a NEW bolt body and bolt-head will solve the problem. If not, it is getting to the time to consider permanent retirement of that action.

Those with "well loved" No4 Mk1* actions may encounter chipping of the corners of the bolt-head removal cutout. As this chipping extends, in company with bolt and body wear, the rate of bolt-head "escape" rapidly rises. It appears that at the time of manufacture, it was not deemed necessary to chamfer the ends of the tiny rib of the bolt-head to help the bolt-head through the gap. Maybe some Canadians can chime in here. In a huge Ordnance system, during rebuilds / "heavy" maintenance, one simply wrote off the worn / damaged body and other components and got fresh(er) ones from the parts bins.

I have seen a couple of chipped 1* bodies repaired with the aid of a TIG welder and a tiny grinder like a Dremel or Foredom, but that simply ignores the wear of other surfaces and components that caused the situation in the first place.

I have to think that if action bodies actually stretched over time we'd see a lot of cracked ones. And we don't.

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Originally Posted by Brian Dick

Please don't take offense but "known fact"? No offense to gunboards either but I try to look at it from time to time and the crap on there is so overwhelming that i finally gave up.

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I think Pocketshaver was referring to 'various gunboards' (various forums) rather than THE Gunboards forum.

......pocketshaver also put 'known fact' in inverted commas, suggesting he didn't necessarily believe it himself........at least to me that seemed implicit.

With the rear-locking SVT 40 the Soviets determined that action stretch upon firing is measurable and contributed significantly to headspace issues- but if the elastic limit isn't exceeded it simply returns to original dimensions after each shot. The extensional stress is distributed through a lot of metal in both sides of the body and is, obviously, designed not to fail. The stress at the locking lug shoulders in the body is focussed on a rather small area which, I gather, lead to permanent deformation in that area and the ultimate demise of the body. "Stretch" is not what is happening.

Ridolpho (amateur engineer/ professional geologist)

Well put, Ridolpho. There seems to be much confusion between "stretch" and "deformation" (or perhaps between "elastic" and "plastic").

Thank you all, lots of interesting info and history all in one. Glad I asked.

I had one guy claimed the bolts compressed! Wow, really?

"Yes, you can compress steel, just hammer on it and see".

Uh sorry bud, that is called displacement, whole different thing.

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Originally Posted by RC20

. . . I had one guy claimed the bolts compressed! Wow, really? . . .

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Yes, really. On firing, chamber pressure transmitted through the case head compresses the portion of the bolt between the bolt face and the locking lugs. Normally, when pressure abates, the bolt returns to its original dimensions. This is what we call an "elastic" process. If pressure is grossly excessive parts can be permanently deformed - a "plastic" process.

It may be helpful to think of what happens to a simple coil extension spring. Pull the ends away from each other less than the maximum design extension and it happily returns to its original length (elasticity at work). Extend it too far and it won't return to its original length (plastic deformation - or even fracture). Unlike the bolt and receiver of a Lee-Enfield during firing, this is readily seen by human eyes - but the same processes can indeed occur even though we can't ordinarily observe them with only our unaided senses.

Search for "elastic vs. plastic" and you can find all sorts of good stuff like this example -

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Elastic vs Plastic Deformation

Deformation is the action or process of deforming or distorting. When a force is applied to an object, the object will either compress or stretch as a response to the force. In mechanics, the force applied to a unit area is called stress. The extent of stretching or compressing (as a response to the stress) is called strain. Every material responds differently to stress. The response is highly dependent on the chemical bond type of the substance. Deformations can be elastic or plastic based on what happens after the stress is released. Elastic deformation is the deformation that disappears upon removal of the external forces causing the alteration and the stress associated with it. Plastic deformation is a permanent deformation or change in shape of a solid body without fracture under the action of a sustained force. The main difference between elastic deformation and plastic deformation is that elastic deformation is reversible whereas plastic deformation is irreversible.

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as far as bolt compression goes, and lock up issues. Look at the rear locking bolt on the lever action rifle. EVERY reloading source says a lever action cartridge HAS to be full length sized after each firing, due to the fact that the rear ward displacement of the entire bolt upon the rear locking lugs causes the cartridge case to stretch to far to allow it to rechamber safely/at all unless full length sized.

Using the SVT 40 analogy again, the Soviets concluded elastic deformation of the receiver (and other parts including bolt) could add around 0.008" to the measurable dimensional headspace for a given rifle. They were greatly interested in this because case ruptures were an issue during the early development of the rifle. This info is on pg 176 of the book by R. Chumak, unfortunately only available in Russian. In my own small collection of SVT 40's you can see the progressive addition of meat to the receiver sidewalls from 1940 to 1944, presumably to stiffen it up.

Ridolpho

I wonder if someone could resurrect an old thread that I wrote a couple(?) of years ago relating to the mysterious stretching of rifle bodies and.......... I really don't want to go through it all again but it does ask some valid questions relating to what exactly are you stretching it against pray tell.
Peter Laidler.

This has taken a turn, so I appreciate the responses and will go over to the disagreement part.

You can't have steel compress. Its possible a receiver can stretch and spring back. I don't think so but put that in maybe.

If on firing you have increase head space, you may be moving the lugs to full tight, the bolt may compress if it has a floating head in that the spaces get taken up (this assume a rear locking lugs, a front locking floater will not do that)

But if it opens up and stays opened up, then its plastic deformation of the receiver and it will continue to grow on each shot. Once you hit plastic it does not stop (assuming save force that put it there)

A cap screw (fastener) has to have threads cut into it to be a spring. A rifle had no parts in it in the receiver or the bolt remotely like that.

An extreme example is pipe testing. You don't test with AIR. Why? Its compressible and will continue to expand on release (messy if not deadly)

You pump the pipe full of WATER (which is partially non compressible) and then you top it up with air. Pipe ruptures, small release, no spread, no death.

A rifle bolt MIGHT flex, but its not going to compress.