Leaving a gap at the shoulder for mud and crud to make chambering easier in trench conditions would make sense...
...there has to be some reason why the chamber is shaped like that...??
1913 SMLE Chamber Section
Moderator: dromia
Re: 1913 SMLE Chamber Section
IIRC the precise reason for the specific dimension of the chamber shoulder is not in any known remaining document.
We have the problem that there is almost nothing left in the public domain of the design and manufacture records for Enfield rifles. The three main authoritative (i.e. written by those involved first hand in the design and manufacture of the weapon system, not just second hand accounts by others) resources are the Text Book of Small Arms (various editions), Maj EGB Reynolds' "The Lee Enfield", and the various military List of Changes - and the LoC only lists changes to military specifications, but not the reasons for them.
The TBoSA and Reynolds discuss two considerations for chamber (neck) shape: (1) primary extraction - for which the whole case is tapered, and (2) case oiling and gas sealing during firing.
The primary extraction is self-evident: the case had to be tapered in order to reduce the distance it had to be extracted to get it to "unstick" from the chamber walls. One of the well known Enfield design strengths is its powerful primary extraction camming action on bolt-opening.
The "case oiling" is likely the real reason for the gap at the shoulder. Ammunition had been traditionally lubricated/waxed anyway in black powder days (i.e. on the lead bullet, and to preserve paper cases) but, when high velocity/ small calibre/ brass case ammunition was developed, it was discovered that oil had a significant effect on gas seal around the case neck. Briefly, it was thought that oil or wax on a case body was squeezed forward as the case expanded from rear to front, and that it ended up compressed in the gap around the case shoulder, the bullet/case step, and the bullet/barrel lead interface. Tests showed that oiled ammunition grouped better in many/most rifles, and it was deduced that the oil was assisting the gas seal around the bullet as it "set up" into the rifling.
Many manufacturers oiled/waxed the ammunition as standard (South African and Yugloslav ammo was often waxed right up until modern times), and the "external" coating was thought necessary on the later MkVIII boat-tail bullets (a development of the inter-war .303 "magnum" and streamline target bullets) as the "internal" method of having beeswax in the cannelure of a flat base bullet was not possible due to the changed bullet seating.
[Note: its a great Enfield myth that ammunition MUST be free of oil/water. In fact its quite the contrary - ammunition was often manufactured with a wax coating, and the service pressure specification for .303 assumes that the case is lubricated. "Dry" ammunition in fact delivers about half the bolt thrust of the normal service specification. Ergo, "dry" ammunition gives the rifle an easy time, but its not actually the presumed standard state for which the rifle was designed.]
A further, third, consideration is hinted at in TBoSA, but not specifically linked to case neck design - this is a discussion of the stages of case expansion, the qualities and properties of constituent brass, the mechanism for release of the bullet (from the tight clamp of the case neck), etc. The inference is that the chamber neck design might have a gap to accommodate the final phase of case expansion as it releases the bullet. It may be that the range of bullet retaining methods used during mass production in WW1 (crimping, pitch sealing, etc) may have necessitated a relieving of the chamber shoulder to allow the brass "somewhere to go" to facilitate release of the bullet.
Legend has it that the Enfield chamber was enlarged to allow ingress of mud during WW1 conditions. Whilst its clear that the rifle boltway-bolt clearance was enlarged (due to pre-war rifles sticking during heavy use), IIRC there is no specific mention that the chamber was enlarged to allow inclusion of mud or foreign bodies. I have a feeling that the chamber was enlarged due to "WW1 conditions", but that the "conditions" might be to do with ammunition manufacture variations (eg bullet seating and sealing) rather than "environmental" conditions.
But hey, I might be talking out of my arrse! As I said, the sources are limited, so its necessary to make deductions from what is written. One thing you can be certain of is that every single tiny feature of an Enfield had some design purpose.
We have the problem that there is almost nothing left in the public domain of the design and manufacture records for Enfield rifles. The three main authoritative (i.e. written by those involved first hand in the design and manufacture of the weapon system, not just second hand accounts by others) resources are the Text Book of Small Arms (various editions), Maj EGB Reynolds' "The Lee Enfield", and the various military List of Changes - and the LoC only lists changes to military specifications, but not the reasons for them.
The TBoSA and Reynolds discuss two considerations for chamber (neck) shape: (1) primary extraction - for which the whole case is tapered, and (2) case oiling and gas sealing during firing.
The primary extraction is self-evident: the case had to be tapered in order to reduce the distance it had to be extracted to get it to "unstick" from the chamber walls. One of the well known Enfield design strengths is its powerful primary extraction camming action on bolt-opening.
The "case oiling" is likely the real reason for the gap at the shoulder. Ammunition had been traditionally lubricated/waxed anyway in black powder days (i.e. on the lead bullet, and to preserve paper cases) but, when high velocity/ small calibre/ brass case ammunition was developed, it was discovered that oil had a significant effect on gas seal around the case neck. Briefly, it was thought that oil or wax on a case body was squeezed forward as the case expanded from rear to front, and that it ended up compressed in the gap around the case shoulder, the bullet/case step, and the bullet/barrel lead interface. Tests showed that oiled ammunition grouped better in many/most rifles, and it was deduced that the oil was assisting the gas seal around the bullet as it "set up" into the rifling.
Many manufacturers oiled/waxed the ammunition as standard (South African and Yugloslav ammo was often waxed right up until modern times), and the "external" coating was thought necessary on the later MkVIII boat-tail bullets (a development of the inter-war .303 "magnum" and streamline target bullets) as the "internal" method of having beeswax in the cannelure of a flat base bullet was not possible due to the changed bullet seating.
[Note: its a great Enfield myth that ammunition MUST be free of oil/water. In fact its quite the contrary - ammunition was often manufactured with a wax coating, and the service pressure specification for .303 assumes that the case is lubricated. "Dry" ammunition in fact delivers about half the bolt thrust of the normal service specification. Ergo, "dry" ammunition gives the rifle an easy time, but its not actually the presumed standard state for which the rifle was designed.]
A further, third, consideration is hinted at in TBoSA, but not specifically linked to case neck design - this is a discussion of the stages of case expansion, the qualities and properties of constituent brass, the mechanism for release of the bullet (from the tight clamp of the case neck), etc. The inference is that the chamber neck design might have a gap to accommodate the final phase of case expansion as it releases the bullet. It may be that the range of bullet retaining methods used during mass production in WW1 (crimping, pitch sealing, etc) may have necessitated a relieving of the chamber shoulder to allow the brass "somewhere to go" to facilitate release of the bullet.
Legend has it that the Enfield chamber was enlarged to allow ingress of mud during WW1 conditions. Whilst its clear that the rifle boltway-bolt clearance was enlarged (due to pre-war rifles sticking during heavy use), IIRC there is no specific mention that the chamber was enlarged to allow inclusion of mud or foreign bodies. I have a feeling that the chamber was enlarged due to "WW1 conditions", but that the "conditions" might be to do with ammunition manufacture variations (eg bullet seating and sealing) rather than "environmental" conditions.
But hey, I might be talking out of my arrse! As I said, the sources are limited, so its necessary to make deductions from what is written. One thing you can be certain of is that every single tiny feature of an Enfield had some design purpose.
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huntervixen
Re: 1913 SMLE Chamber Section
As ever, always an "Enfield Education" when you contribute Rearlugs, many thanks for that .. Your thoughts on variations of mass produced ammo are certainly an equally valid reason for relieving the chamber.... a sort of one size fits all Wartime solution.Rearlugs wrote:IIRC the precise reason for the specific dimension of the chamber shoulder is not in any known remaining document.
We have the problem that there is almost nothing left in the public domain of the design and manufacture records for Enfield rifles. The three main authoritative (i.e. written by those involved first hand in the design and manufacture of the weapon system, not just second hand accounts by others) resources are the Text Book of Small Arms (various editions), Maj EGB Reynolds' "The Lee Enfield", and the various military List of Changes - and the LoC only lists changes to military specifications, but not the reasons for them.
The TBoSA and Reynolds discuss two considerations for chamber (neck) shape: (1) primary extraction - for which the whole case is tapered, and (2) case oiling and gas sealing during firing.
The primary extraction is self-evident: the case had to be tapered in order to reduce the distance it had to be extracted to get it to "unstick" from the chamber walls. One of the well known Enfield design strengths is its powerful primary extraction camming action on bolt-opening.
The "case oiling" is likely the real reason for the gap at the shoulder. Ammunition had been traditionally lubricated/waxed anyway in black powder days (i.e. on the lead bullet, and to preserve paper cases) but, when high velocity/ small calibre/ brass case ammunition was developed, it was discovered that oil had a significant effect on gas seal around the case neck. Briefly, it was thought that oil or wax on a case body was squeezed forward as the case expanded from rear to front, and that it ended up compressed in the gap around the case shoulder, the bullet/case step, and the bullet/barrel lead interface. Tests showed that oiled ammunition grouped better in many/most rifles, and it was deduced that the oil was assisting the gas seal around the bullet as it "set up" into the rifling.
Many manufacturers oiled/waxed the ammunition as standard (South African and Yugloslav ammo was often waxed right up until modern times), and the "external" coating was thought necessary on the later MkVIII boat-tail bullets (a development of the inter-war .303 "magnum" and streamline target bullets) as the "internal" method of having beeswax in the cannelure of a flat base bullet was not possible due to the changed bullet seating.
[Note: its a great Enfield myth that ammunition MUST be free of oil/water. In fact its quite the contrary - ammunition was often manufactured with a wax coating, and the service pressure specification for .303 assumes that the case is lubricated. "Dry" ammunition in fact delivers about half the bolt thrust of the normal service specification. Ergo, "dry" ammunition gives the rifle an easy time, but its not actually the presumed standard state for which the rifle was designed.]
A further, third, consideration is hinted at in TBoSA, but not specifically linked to case neck design - this is a discussion of the stages of case expansion, the qualities and properties of constituent brass, the mechanism for release of the bullet (from the tight clamp of the case neck), etc. The inference is that the chamber neck design might have a gap to accommodate the final phase of case expansion as it releases the bullet. It may be that the range of bullet retaining methods used during mass production in WW1 (crimping, pitch sealing, etc) may have necessitated a relieving of the chamber shoulder to allow the brass "somewhere to go" to facilitate release of the bullet.
Legend has it that the Enfield chamber was enlarged to allow ingress of mud during WW1 conditions. Whilst its clear that the rifle boltway-bolt clearance was enlarged (due to pre-war rifles sticking during heavy use), IIRC there is no specific mention that the chamber was enlarged to allow inclusion of mud or foreign bodies. I have a feeling that the chamber was enlarged due to "WW1 conditions", but that the "conditions" might be to do with ammunition manufacture variations (eg bullet seating and sealing) rather than "environmental" conditions.
But hey, I might be talking out of my arrse! As I said, the sources are limited, so its necessary to make deductions from what is written. One thing you can be certain of is that every single tiny feature of an Enfield had some design purpose.
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