.303 British Case Separations - Causes and Cures
The combination of British Lee-Enfield rifles, odd chambers and thin brass have made this round my all time worst destroyer of brass - caused by partial & complete head separations.
1.The Lee-Enfield action is a bit elastic and that can add to the damage that causes the separations. I have calculated the momentary stretch with full power loads on the #4 Mk1 at
2. In addition some Lee-Enfields can have a good bit of head space that can add to case stretching if you persist with FL sizing.
3. The chambers are both extra large in diameter and extra long to the shoulder as compared to most ammo. Brass when fired has to stretch to fit the chamber to the shoulder and it has to expand diametrally to fit the chamber diameter. The poor diametral fit causes a lot of stretching at the solid head junction with the case wall. You can identify this stretch by the prominent pressure ring step in the case where the solid head joins the case wall.
4. The Lee-Enfield chambers usually measure .460 at the big end of the chamber. US brass typically measures .450 to .452 at the solid head just ahead of the rim. That is too much expansion coupled with the other things that add to the damage. Acceptable expansion of the case would be more like .004 or less at the case head pressure ring step.
Common Brass faults
5. US made brass is light weight in the case wall thickness and US made brass, especially Remington, is way shorter than the chambers at the shoulder location.
6. The over length .303 chambers did what the Brits needed but they stink for people trying to make expensive brass last. If you examine both CIP and SAAMI drawings for the cartridges and the chambers you will find they are very much like any other cartridge design where the cartridge actually looks like the chamber.
However the British chambers have been impossible to document. It seems the Brits do not really have fully dimensioned and toleranced drawings for both the ammo and the chambers. If you collect enough once fired .303 brass you will eventually see a wide range of chambers including some that qualify as clown chambers.
How to deal with all of the above?
Start out with the best brass for the job and right now that is PPU. The head of PPU brass is larger in diameter at .454 to .455 and that will reduce the radial stretching. The PPU brass has a longer shoulder location which helps reduce stretching. It is also thicker in the case walls which helps resist stretching.
You can try the following to see how much they help case life. One through four will only be needed for the 1st fire forming shot.
1. Use small O rings or rubber bands around the case head to take up any head space by forcing the case against the bolt face.
2. Expand the neck on new brass to about .35 or .375 cal. and neck back down to give a new shoulder with positive contact when the bolt is closed. This prevents so much of the shoulder from having to blow forward on the first shot.
3. Wrap the case head with a .150 wide strip of .003 to .004 thick tape just ahead of the rim. Use enough tape (probably 1 full wrap) to center the case head in the chamber so the step at the solid head is spread around the full diameter and is not concentrated on one side by the extractor.
4. If you are an advanced and motivated hand loader you can try using your FL die to hydroform the case body so the shoulder expands radially rather than stretching longitudinally. This is one of my next projects.
5. For those that are familiar with a lot of fire forming, smooth chambers help. If you know how to polish a chamber without damaging it a light polish does no harm.
6. You can apply a very light film of oil to help the case form without sticking to the chamber. This prevent the case from grabbing the chamber and stretching at the first shot.
Once you have fired your brass the best you can do for it next is to keep it clean and neck size it with a dedicated NECK die such as the Lee Collet neck die or a common die for a fatter case like a .308 Win. with the proper .303 sized expander. Size only the upper 75% of the neck and do not touch the shoulder. Remember the Lee-Enfield chambers are nowhere close to the SAAMI dimensions of the US made loading dies. Once you get the case body expanded to fit your chamber you never want to size it again.
Finally keep your loads mild so you never have to FL size it because I guarantee the inside of your FL die is not going to match your chamber unless you get a custom die made to match your chamber.
Keep track of your brass. Examine it carefully before each loading for impending head separations.
For reference only
Case forming adventures tried
1. .30-40 Krag
About 20 years ago Krag brass made by RP and WW was about .455 on the head. I tried some of it and it worked OK for the most part. I did have one old case that separated without ever expanding the Krag shoulder forward. This one case might have been hinting that my pressure was too low and my powder was too slow expand the case before it pulled in two. The latest reports I have indicate that recent Krag brass is the same size at the head as current .303 brass. Check with a micrometer if you have any Krag brass.
I still have a few Krag cases in a box of ammo with about 12 different .303 head stamps
2. .444 Marlin
This brass is about the right length but requires several steps to form the neck. The case head is also too large at .464 to .466 so it has to be swaged or turned down. Swaging the head will split the common .44 magnum dies that I used. I found that the case walls of the .444 are significantly thicker at the case head junction.
.444 brass is so expensive now that I would not even bother. It did make long lasting brass and I am still shooting a box of it.
3. .405 Win brass made by Hornady
This was just a fun learning experience with 3 pieces. The .405 brass is tough and required several intermediate steps to form. The necks were too thick to chamber with a .312 bullet so they were turned and annealed.
The rims are right at the max that my rifle will close on. One of the rims was too thick and needed thinning from the front of the rim. These are very tough heavy cases that would last a long time. But they are very expensive and require a lot of work. The best thing is the case heads are .458 to .459 and will just barely fit the chambers with almost no expansion. You would have to polish out the base of a FL die to avoid sizing the solid head of these cases.
If all of these things don’t work the best I can recommend is some permanent modification of the chamber or rebarreling of the rifle. I have an idea for one change but I will not discuss it since I have not yet tried it.
I have bought once fired R-P and Norma brass that had partial head separations from being fired with the factory loads. This is the only caliber brass that I have ever bought with separations from the first firing of factory ammo. So I will recommend do not get your brass from factory ammo or any once fired brass if you can help it. Some brass is of high quality but it is often damaged by the first shot at full pressure.
Start with new brass and mild loads for longer case life.
Always wear safety glasses with one of these rifles. I have had many case head separations because I was using someone’s once fired brass. I have never had a gas leak but there is always a first time.