Thank you, nice clear (and concise) video - I have just started reloading with my 303 British. After full length resizing I had a case failure - separation and found (was informed) that I only needed to neck size as the cartridges had fire-formed.
You need to be extra careful with 303 British. The chambers are usually larger than the 'specification' and they grow a lot. The case shape and material makes them thin and prone to splitting. The first rifle cartridges I re loaded were 303 British and I had case separation issues. I could only get one re load out of them. I was not neck sizing so hopefully neck sizing can get you a couple extra re loads. Be very cautious and check your brass carefully for thinning and a shiny line on the base of the brass. Good luck.
regardless how much you adjust the die, the collet is only going to close so far up against the brass and the brass against the mandrel even if you cam over. Camming over will not hurt the collet. If you close the die without a case inserted in the collet then you can collapse the collet too much. To fix that if it happens take a small screw driver and open the collet back up. If you don't cam over and rely on just the force Lee recommends, then I ran into necks not sized enough.
Excellent video John. I love this die. I find I have to do a little setup work to most of the Lee stuff I purchase but in the end, the stuff works well for me and is very often a good concept. This neck die there's one of their finest ideas. But man I would never have thought to put anti-seize in there. That's a damn fine idea! Thank you!
Best use would be to full length size with a separate full length die with the expander removed. Set that die to bump your shoulder back .002". Then use the Lee die to size the neck down to give you the correct neck tension you want.. no one these days neck sizes anymore.
Lee mentions "dwell time", apparently the time you keep the collet engaged, presumably to allow the brass neck to settle in for some time. Ever hear of that?
I think a couple second is all it takes. There is a slight amount of spring back after you remove the case form the die. Until the brass gets brittle and then should be annealed.
I love Enfield's and I bet yours is a beauty. 303 definitely stretches the case and leads to separation. Neck sizing is the way to go if you have the tools. My No. 4 MK1* has an over sized chamber and it will stretch the brass no matter what but it is a battle used war rifle. Thank you for watching ad commenting. Have a great day.
@@johnshandloading7907 It is unlikely that there are any more than just a few Lee Enfields that have "an oversize chamber" in civilian hands. That is why both the arsenals that manufactured the rifles and the military gun plumbers that maintained the rifles for the troops at war had go-no go gauges. Headspace could change - thus the numbered bolt heads as you see on your rifle. If your bolt head number is a "3", then you are approaching the scenario where the entire action is no longer in spec. If it was out of spec, in the majority of cases the arsenal would have marked it as a DP rifle and it would not have been released for sale to civilians as surplus. My Long Branch is a "0" bolt head; I see very, very few Lee Enfields with "3" bolt heads and most of those are in pretty ratty shape to begin with. Most are a "1" or "2". Fun anecdotal fact: one of the most accurate rifles (and the owner one of the best shots) I saw in Service Rifle competition had a "3" bolt head. Didn't seem to matter which military ball and lot was being issued for that match - that Lee Enfield would stack them when the owner did his part. He would have been aghast if anyone had suggested he have it rebarrelled with a replacement Lee Enfield barrel. But the rifle wasn't manufactured with "an oversize chamber". It was manufactured with a military chamber intended for military use, with specifications that would allow muddy ammunition to chamber in the muddy trenches of The Somme, Vimy Ridge, etc. Or verdigris covered ammunition stored for years in some monsoon drenched humid backwater munitions dump in India. In other words, the British Empire and their Commonwealth arsenals in Canada, Australia, India, etc did not cut chambers to eject fired brass specified for American reloading dies that would be manufactured decades later. If you are having problems with brass stretching in any Lee Enfield rifle while reloading, with respect, you aren't doing it right. You're partially getting it right using the collet die, but proper brass preparation starts before that. Starting with which brass you choose to use if you're a serious reloader for the Lee Enfield variants. With the disappearance of the surplus Greek HXP ball ammo manufactured in the mid 1980's (now coveted like gold dust by Service Rifle competitors), Privi Partizan is head and shoulders above anything else available that I'm aware of here in the US where quality is concerned. Comparisons to dimensions (particularly rim dimensions) of Commonwealth military ball ammo from the 1920s through 1980's, PP looks as though they purposefully intended to duplicate Commonwealth military brass specifications. Civilian brass from Winchester et al is not even close when measured and compared. It's a very simple process reloaders will quickly grasp once you get their heads wrapped around accepting that there is nothing oversize about their Lee Enfield's chamber - it's the undersized American reloading dies designed for American chambered rifles that you need to deal with. Even if you don't want to bother taking a deliberate approach to preparing brass so there is no initial stretching of brass, you simply need to think of it as reloading fireformed brass. Best regards.
Definitely take it apart and clean it really well, then polish the surfaces that can bind. Last thing you have to put anti seize compound in the top so it does not get stuck anymore. I had that problem with mine. It even wrecked some cases from binding.
Depends on the case and the rifle. The bolt can be a little sticky closing on the second or third time of neck resize simply because it is very close to the same size as the chamber walls. I would say 3 or 4 times on average before needing a full length re sizing. . Then a full length resize and trim is in order. But you still have to measure the length after each sizing, even a neck sizing to make sure the case is not getting too long. I hope that helps.
@@johnshandloading7907 I've been full sizing with Lapua brass 223, but wanted to give neck sizing a shot since I have the set. At six resizing it's noticably harder to squish the brass from when I started. I want to see if throwing in a few neck sizings will prolong brass life a bit. I guess this phenomenon is 'work hardening'? Thanks.
@@xNevikKx Yes. I think your brass needs to be annealed, full length sized and then trimmed. Definitely sounds work hardened and will be so brittle it cracks or breaks. A torch and a socket on a electric drill works for annealing for me.
Hello John, I have the following problem whit Collet Die. I follow the description exactly but when i squeeze neck i have bump the shoulders exactly 0,004". Have you measured if it is with you bump?
I never measured the bump back and never had any issues with the results on target. I suggest backing the die out slightly and seeing if that helps. Are you trying to only push back .002? The distance from the shell holder to the inside of the die will change the amount of resizing done.
You may have a press that cams over. This creates to much pressure on the neck and the shoulder will collapse (bulge) ruining the case. Back out the die and try over again. Use your calibers and check the inside neck diameter .
@@gascheck8151 nope. A press that cams over does not create too much pressure on the neck. And the die does not bump the shoulder back. At all. If shoulders are collapsing, you probably raised the ram on an empty die. The collet stuck closed. Take it apart and open the collet with a small screwdriver. From there on, don't ever raise the ram without a case in the shellholder. A press that cams over is actually better than a Lee press because you don't have to "guesstimate" how much 25 lbs of pressure is. The Lee Collet Neck Die is arguably the greatest invention in all of reloading. That's why it's on the cover of Lee's reloading manual.
@johnshandloading7907 "You need to be extra careful with 303 British. The chambers are usually larger than the 'specification' and they grow a lot." The chambers are NOT larger than the specification - that is one of our American Urban Legends in the reloading subject matter field. The chambers have some variations due to different reamers and wear over periods of manufacture and different arsenal manufacturers. But they were cut to the specs that came from the Pattern Room - the Commonwealth wartime versions that long predated our American SAAMI (and CIP in Europe). If there is actually something out of spec, it is what SAAMI chose for dimensions for reloading dies that had zero consideration for the original Commonwealth British military spec chambers instead of American hunting rifle chambers. This is where the handloader's problem lies (more accurately, potential problem): 1. The English Empire that spanned the globe in the late 1880's when the .303 British and their Enfield rifles were introduced required ammunition stored for years in all sorts of backwater colonial nations where the weather could be unrelenting dry heat of deserts in Afghanistan versus places like India with monsoons and unending humidity. Ammunition in those conditions can develop verdigris on the surface, swelling, etc. The last thing soldiers at war need is to be issued ammunition that will not chamber. So the Brits specified chambers cut so that long stored ammunition WOULD chamber after being in colonial storage for years. That was exacerbated in WWI when both living in mud filled trenches and substandard emergency wartime ammunition resulted in there still being that worse case scenario: ammunition that would not chamber. The response was to cycle existing Lee Enfields for an FTR to further increase chamber dimensions along with new chamber specifications for Lee Enfields coming from the arsenals to go to war. Sidebar: this is what killed the Canadian Ross Rifle - not some inherent defect; they had relatively tight chambers we would consider cut for hunting/target accuracy (or fighting the Boers at long range in Africa about the same time). They could not chamber substandard/muddy ammunition. 2. The British Empire had exactly zero concern regarding their chamber designs for the advent of handloading that would come decades later. Fired cases were left were they fell, unless on a military range. The SAAMI geniuses, on the other hand, never gave any consideration to the military specifications of Lee Enfield chambers manufactured over a 60 year period, and the tens of thousands of surplus Lee Enfields in use around the world. If anything, they gave consideration to American manufactured rifles chambered in .303 British for civilian use. I have both a Winchester 1895 and Savage 99 lever actions in .303 British, both manufactured prior to WWI. I did cerrosafe chamber casts for both prior to beginning to work up cast bullet loads for both (thumbs up to Accurate Moulds for his precision custom molds that drop bullets to your specs). Those chambers are far, far skinnier than any Lee Enfield I have done casts on when measured. That includes my post war 1950 Long Branch that I purchased unissued and shot in Service Rifle competition for years. The post war 1950 Long Branches are the best of the best when it comes to quality in the No. 4 Mk1. 3. So the "out of spec/excessive headspace" issue is in fact an issue of handloaders not understanding their dies were manufactured with brass from American chambers in mind. They faithfully follow the die manufacturer's instructions to insert the die until it touches the die holder, etc, resize, and then reload. Each time they do it, followed by firing it again, they are in an a cycle of excessively working the brass - resulting in each time the case stretches again and again. And this is why brass reloaded in this manner doesn't last very long - why would anyone expect it to when reloaded in this way? To eliminate this stretch/resize/stretch/resize cycle, you simply change how you reload. Unless you're knowledgeable enough/care enough to prepare new brass for reloading, you simply adjust your sizing die down just enough to give you a crush fit when chambering the resized case, no more than that. You are essentially working with fireformed cases from your rifle - and if you have multiple military rifles, each rifle should have it's own bunch of brass. And this is where the Lee Collet Die is so valuable to those who reload for military .303 British rifles in particular. That fire formed brass from your rifle only gets reworked on the neck with the collet die, there is no work hardening or repeated resizing/stretching of the case body. Eventually, the brass will need a bit of a body bump. Brass done this way will last every bit as long as any brass you reload for in any of our American hunting calibers. 4. To maximize brass life AND accuracy in the .303 British for military rifles, start with virgin new brass. Most American manufactured brass has far thinner rims (there's your headspace) compared to military rim thickness. In comparing military ball ammo I've obtained from the 1920s - 1980s period, the commercial brass that closest matches military .303 ball is Privi Partizan. It is usually easily obtainable; the brass dimensions were probably designed to replicate military ball ammunition. Of military brass, the Greek HXP ball ammo from the mid 80's was the highest quality, extremely accurate, and cheap like borscht when it was available. When Lee Enfield rifle owners realized that - especially those still involved in competition using Lee Enfield rifles - it disappeared and asking prices skyrocketed as it was snapped up and availability eventually disappeared. So, start with your new brass; you are going to create a false shoulder so that when your new brass is first fired, it is supported by the base of the head firmly against the bolt face while the false shoulder is in firm contact with the front of the chamber. This leaves the brass with no way to stretch forward, but instead only expand outward when fired. Buy a Lyman .33 neck expander; this will work the new case necks the least; a .35 neck expander isn't necessary and works the neck more than necessary. Lubricate the inside of the cases with dry graphite (or whatever you prefer). Run the cases through the neck expander. Now run them through your full length resizer (or neck resizer), starting with just a little bit of resizing back to .303 size at the top. Making small adjustments each time, continue resizing down the neck, trying to chamber the partially resized case after each adjustment. At first the brass will not chamber - the false shoulder you have formed is too far forward to allow the bolt to close. When you have the false shoulder moved far enough back, you now have brass that when loaded will not stretch even once when first fired. And the resulting fire formed brass is just right for THAT particular rifle. And again, this is a case where resizing using the Lee Collet Die is particularly useful in .303 British military rifles. You don't do all that work and then resize that brass with reloading dies following their instructions. You resize the neck only, using the collet die. Eventually you'll have to bump the case a bit before returning back to collet die resizing, but it will take a few firings before that happens. 5. To further increase brass life (and probably accuracy if using a Lee Enfield in competition), anneal the case mouths to eliminate the stress and work hardening from the neck resizing. Some do it every three or four firings; as it takes so little time, I do it every time I prepare the fired brass for reloading after finishing resizing. I use the method of an alcohol lamp (cheap like borscht on Amazon) while rolling the case between my fingers until too hot too hold, then drop on a towel. No need to drop in water - and you can't "quench" brass. That's not the most accurate way to anneal, but it doesn't have the potential risk of overheating the brass with a propane torch and it doesn't cost hundreds of dollars like the electronic annealing machines -and it's a low cost/low time investment.
Thank you, nice clear (and concise) video - I have just started reloading with my 303 British. After full length resizing I had a case failure - separation and found (was informed) that I only needed to neck size as the cartridges had fire-formed.
You need to be extra careful with 303 British. The chambers are usually larger than the 'specification' and they grow a lot. The case shape and material makes them thin and prone to splitting. The first rifle cartridges I re loaded were 303 British and I had case separation issues. I could only get one re load out of them. I was not neck sizing so hopefully neck sizing can get you a couple extra re loads. Be very cautious and check your brass carefully for thinning and a shiny line on the base of the brass. Good luck.
@@johnshandloading7907 Thanks, I have now found a local mentor and will see how it goes, if you are interested I will let you know.
@@DavidWhelbourn I would love to know. Please keep me in the loop. Thanks.
regardless how much you adjust the die, the collet is only going to close so far up against the brass and the brass against the mandrel even if you cam over. Camming over will not hurt the collet. If you close the die without a case inserted in the collet then you can collapse the collet too much. To fix that if it happens take a small screw driver and open the collet back up. If you don't cam over and rely on just the force Lee recommends, then I ran into necks not sized enough.
Excellent video John. I love this die. I find I have to do a little setup work to most of the Lee stuff I purchase but in the end, the stuff works well for me and is very often a good concept. This neck die there's one of their finest ideas. But man I would never have thought to put anti-seize in there. That's a damn fine idea! Thank you!
Glad the idea helped you. It works well on mine.
Great demonstration John. I have the ultimate die sets but usually FLS for my hunting ammo. I need to do more with the collet die.
Best use would be to full length size with a separate full length die with the expander removed. Set that die to bump your shoulder back .002". Then use the Lee die to size the neck down to give you the correct neck tension you want.. no one these days neck sizes anymore.
Lee mentions "dwell time", apparently the time you keep the collet engaged, presumably to allow the brass neck to settle in for some time. Ever hear of that?
I think a couple second is all it takes. There is a slight amount of spring back after you remove the case form the die. Until the brass gets brittle and then should be annealed.
@@johnshandloading7907 Thanks John!
Great video explaining it 👍🇺🇸
I've been reloading since the 1970's and never neck sized. Then I got this unissued No 4 MK 2 Enfield. Long story short....... now I neck size. LOL
I love Enfield's and I bet yours is a beauty. 303 definitely stretches the case and leads to separation. Neck sizing is the way to go if you have the tools. My No. 4 MK1* has an over sized chamber and it will stretch the brass no matter what but it is a battle used war rifle. Thank you for watching ad commenting. Have a great day.
@@johnshandloading7907 It is unlikely that there are any more than just a few Lee Enfields that have "an oversize chamber" in civilian hands. That is why both the arsenals that manufactured the rifles and the military gun plumbers that maintained the rifles for the troops at war had go-no go gauges.
Headspace could change - thus the numbered bolt heads as you see on your rifle. If your bolt head number is a "3", then you are approaching the scenario where the entire action is no longer in spec. If it was out of spec, in the majority of cases the arsenal would have marked it as a DP rifle and it would not have been released for sale to civilians as surplus. My Long Branch is a "0" bolt head; I see very, very few Lee Enfields with "3" bolt heads and most of those are in pretty ratty shape to begin with. Most are a "1" or "2".
Fun anecdotal fact: one of the most accurate rifles (and the owner one of the best shots) I saw in Service Rifle competition had a "3" bolt head. Didn't seem to matter which military ball and lot was being issued for that match - that Lee Enfield would stack them when the owner did his part. He would have been aghast if anyone had suggested he have it rebarrelled with a replacement Lee Enfield barrel.
But the rifle wasn't manufactured with "an oversize chamber". It was manufactured with a military chamber intended for military use, with specifications that would allow muddy ammunition to chamber in the muddy trenches of The Somme, Vimy Ridge, etc. Or verdigris covered ammunition stored for years in some monsoon drenched humid backwater munitions dump in India.
In other words, the British Empire and their Commonwealth arsenals in Canada, Australia, India, etc did not cut chambers to eject fired brass specified for American reloading dies that would be manufactured decades later.
If you are having problems with brass stretching in any Lee Enfield rifle while reloading, with respect, you aren't doing it right. You're partially getting it right using the collet die, but proper brass preparation starts before that.
Starting with which brass you choose to use if you're a serious reloader for the Lee Enfield variants. With the disappearance of the surplus Greek HXP ball ammo manufactured in the mid 1980's (now coveted like gold dust by Service Rifle competitors), Privi Partizan is head and shoulders above anything else available that I'm aware of here in the US where quality is concerned. Comparisons to dimensions (particularly rim dimensions) of Commonwealth military ball ammo from the 1920s through 1980's, PP looks as though they purposefully intended to duplicate Commonwealth military brass specifications. Civilian brass from Winchester et al is not even close when measured and compared.
It's a very simple process reloaders will quickly grasp once you get their heads wrapped around accepting that there is nothing oversize about their Lee Enfield's chamber - it's the undersized American reloading dies designed for American chambered rifles that you need to deal with. Even if you don't want to bother taking a deliberate approach to preparing brass so there is no initial stretching of brass, you simply need to think of it as reloading fireformed brass.
Best regards.
I have to polish mine up It leaves scratch’s on the neck 👍👍 thanks for sharing
Definitely take it apart and clean it really well, then polish the surfaces that can bind. Last thing you have to put anti seize compound in the top so it does not get stuck anymore. I had that problem with mine. It even wrecked some cases from binding.
Neck sizing is something I've never tried .
How many times can you neck size before your bolt starts getting hard to close, if any?
Depends on the case and the rifle. The bolt can be a little sticky closing on the second or third time of neck resize simply because it is very close to the same size as the chamber walls. I would say 3 or 4 times on average before needing a full length re sizing. . Then a full length resize and trim is in order. But you still have to measure the length after each sizing, even a neck sizing to make sure the case is not getting too long. I hope that helps.
@@johnshandloading7907 I've been full sizing with Lapua brass 223, but wanted to give neck sizing a shot since I have the set. At six resizing it's noticably harder to squish the brass from when I started. I want to see if throwing in a few neck sizings will prolong brass life a bit. I guess this phenomenon is 'work hardening'? Thanks.
@@xNevikKx Yes. I think your brass needs to be annealed, full length sized and then trimmed. Definitely sounds work hardened and will be so brittle it cracks or breaks. A torch and a socket on a electric drill works for annealing for me.
Hello John, I have the following problem whit Collet Die. I follow the description exactly but when i squeeze neck i have bump the shoulders exactly 0,004". Have you measured if it is with you bump?
I never measured the bump back and never had any issues with the results on target. I suggest backing the die out slightly and seeing if that helps. Are you trying to only push back .002? The distance from the shell holder to the inside of the die will change the amount of resizing done.
You may have a press that cams over. This creates to much pressure on the neck and the shoulder will collapse (bulge) ruining the case. Back out the die and try over again. Use your calibers and check the inside neck diameter .
@@gascheck8151 nope. A press that cams over does not create too much pressure on the neck. And the die does not bump the shoulder back. At all. If shoulders are collapsing, you probably raised the ram on an empty die. The collet stuck closed. Take it apart and open the collet with a small screwdriver. From there on, don't ever raise the ram without a case in the shellholder. A press that cams over is actually better than a Lee press because you don't have to "guesstimate" how much 25 lbs of pressure is. The Lee Collet Neck Die is arguably the greatest invention in all of reloading. That's why it's on the cover of Lee's reloading manual.
@johnshandloading7907 "You need to be extra careful with 303 British. The chambers are usually larger than the 'specification' and they grow a lot."
The chambers are NOT larger than the specification - that is one of our American Urban Legends in the reloading subject matter field. The chambers have some variations due to different reamers and wear over periods of manufacture and different arsenal manufacturers. But they were cut to the specs that came from the Pattern Room - the Commonwealth wartime versions that long predated our American SAAMI (and CIP in Europe). If there is actually something out of spec, it is what SAAMI chose for dimensions for reloading dies that had zero consideration for the original Commonwealth British military spec chambers instead of American hunting rifle chambers.
This is where the handloader's problem lies (more accurately, potential problem):
1. The English Empire that spanned the globe in the late 1880's when the .303 British and their Enfield rifles were introduced required ammunition stored for years in all sorts of backwater colonial nations where the weather could be unrelenting dry heat of deserts in Afghanistan versus places like India with monsoons and unending humidity. Ammunition in those conditions can develop verdigris on the surface, swelling, etc. The last thing soldiers at war need is to be issued ammunition that will not chamber.
So the Brits specified chambers cut so that long stored ammunition WOULD chamber after being in colonial storage for years. That was exacerbated in WWI when both living in mud filled trenches and substandard emergency wartime ammunition resulted in there still being that worse case scenario: ammunition that would not chamber. The response was to cycle existing Lee Enfields for an FTR to further increase chamber dimensions along with new chamber specifications for Lee Enfields coming from the arsenals to go to war. Sidebar: this is what killed the Canadian Ross Rifle - not some inherent defect; they had relatively tight chambers we would consider cut for hunting/target accuracy (or fighting the Boers at long range in Africa about the same time). They could not chamber substandard/muddy ammunition.
2. The British Empire had exactly zero concern regarding their chamber designs for the advent of handloading that would come decades later. Fired cases were left were they fell, unless on a military range.
The SAAMI geniuses, on the other hand, never gave any consideration to the military specifications of Lee Enfield chambers manufactured over a 60 year period, and the tens of thousands of surplus Lee Enfields in use around the world. If anything, they gave consideration to American manufactured rifles chambered in .303 British for civilian use.
I have both a Winchester 1895 and Savage 99 lever actions in .303 British, both manufactured prior to WWI. I did cerrosafe chamber casts for both prior to beginning to work up cast bullet loads for both (thumbs up to Accurate Moulds for his precision custom molds that drop bullets to your specs). Those chambers are far, far skinnier than any Lee Enfield I have done casts on when measured. That includes my post war 1950 Long Branch that I purchased unissued and shot in Service Rifle competition for years. The post war 1950 Long Branches are the best of the best when it comes to quality in the No. 4 Mk1.
3. So the "out of spec/excessive headspace" issue is in fact an issue of handloaders not understanding their dies were manufactured with brass from American chambers in mind. They faithfully follow the die manufacturer's instructions to insert the die until it touches the die holder, etc, resize, and then reload. Each time they do it, followed by firing it again, they are in an a cycle of excessively working the brass - resulting in each time the case stretches again and again. And this is why brass reloaded in this manner doesn't last very long - why would anyone expect it to when reloaded in this way?
To eliminate this stretch/resize/stretch/resize cycle, you simply change how you reload. Unless you're knowledgeable enough/care enough to prepare new brass for reloading, you simply adjust your sizing die down just enough to give you a crush fit when chambering the resized case, no more than that. You are essentially working with fireformed cases from your rifle - and if you have multiple military rifles, each rifle should have it's own bunch of brass.
And this is where the Lee Collet Die is so valuable to those who reload for military .303 British rifles in particular. That fire formed brass from your rifle only gets reworked on the neck with the collet die, there is no work hardening or repeated resizing/stretching of the case body. Eventually, the brass will need a bit of a body bump. Brass done this way will last every bit as long as any brass you reload for in any of our American hunting calibers.
4. To maximize brass life AND accuracy in the .303 British for military rifles, start with virgin new brass. Most American manufactured brass has far thinner rims (there's your headspace) compared to military rim thickness. In comparing military ball ammo I've obtained from the 1920s - 1980s period, the commercial brass that closest matches military .303 ball is Privi Partizan. It is usually easily obtainable; the brass dimensions were probably designed to replicate military ball ammunition. Of military brass, the Greek HXP ball ammo from the mid 80's was the highest quality, extremely accurate, and cheap like borscht when it was available. When Lee Enfield rifle owners realized that - especially those still involved in competition using Lee Enfield rifles - it disappeared and asking prices skyrocketed as it was snapped up and availability eventually disappeared.
So, start with your new brass; you are going to create a false shoulder so that when your new brass is first fired, it is supported by the base of the head firmly against the bolt face while the false shoulder is in firm contact with the front of the chamber. This leaves the brass with no way to stretch forward, but instead only expand outward when fired.
Buy a Lyman .33 neck expander; this will work the new case necks the least; a .35 neck expander isn't necessary and works the neck more than necessary. Lubricate the inside of the cases with dry graphite (or whatever you prefer). Run the cases through the neck expander. Now run them through your full length resizer (or neck resizer), starting with just a little bit of resizing back to .303 size at the top. Making small adjustments each time, continue resizing down the neck, trying to chamber the partially resized case after each adjustment. At first the brass will not chamber - the false shoulder you have formed is too far forward to allow the bolt to close.
When you have the false shoulder moved far enough back, you now have brass that when loaded will not stretch even once when first fired. And the resulting fire formed brass is just right for THAT particular rifle. And again, this is a case where resizing using the Lee Collet Die is particularly useful in .303 British military rifles. You don't do all that work and then resize that brass with reloading dies following their instructions. You resize the neck only, using the collet die. Eventually you'll have to bump the case a bit before returning back to collet die resizing, but it will take a few firings before that happens.
5. To further increase brass life (and probably accuracy if using a Lee Enfield in competition), anneal the case mouths to eliminate the stress and work hardening from the neck resizing. Some do it every three or four firings; as it takes so little time, I do it every time I prepare the fired brass for reloading after finishing resizing. I use the method of an alcohol lamp (cheap like borscht on Amazon) while rolling the case between my fingers until too hot too hold, then drop on a towel. No need to drop in water - and you can't "quench" brass. That's not the most accurate way to anneal, but it doesn't have the potential risk of overheating the brass with a propane torch and it doesn't cost hundreds of dollars like the electronic annealing machines -and it's a low cost/low time investment.