Explain the Original SMLE 303 Headspace Situaiton?

[RC20]

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.

Information

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[Brian Dick]

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*.

[bigduke6]

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)

[RC20]

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

[Brian Dick]

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.

[pocketshaver]

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?

[Bruce_in_Oz]

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.

[Patrick Chadwick]

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

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?

[CINDERS]

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

[browningautorifle]

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.

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