Below a rubber O-ring is fitted around the case rim that holds the case against the bolt face. This prevents the base of the case from stretching in the base web area.
[The head clearance or the distance between the bolt face and the base of the case. This allows the case to stretch that amount and cause case head separations.
Below the case is held against the bolt face by the o-ring when fired and prevents the case from stretching.
After this fire forming the case will headspace on the case shoulder.
Below the fired Privi case on the left has a thicker rim and is larger in base diameter. The Greek case is smaller in diameter and has a thinner rim.
Below is a fired case in a Wilson case gage and shows how far the Enfield chamber shoulder is.
Below I use feeler gauges progressively thinner to setup the die until the case chambers on the shoulder.
Below is what happens when you set up the die as per the instructions.
Below from left to right, a new unfired case, a once fired case, and a fired three times that stretched. This was because the die was setup per the instructions and the shoulder pushed back to far.
Below variations in rim thickness.
Below its simple with your Enfield rifle as long as you don't exceed the speed of light.
It seems impossible to overcome the mistaken belief that "excessive headspace" is to blame for short brass life.
I guess you don't read too well. My post said:
"BTW I used recovered primers and so some show a bit of leakage. No biggy there either"
You are so right there. People are really stuck on the idea that when you get those nasty shinny expansion rings after one or two firing it says that there is something wrong with their gun.
The good news is there's nothing wrong with your gun, its your brass .... stupid! Otherwise, how is it that I fire about 15-16 Herters cases in a cross section of four guns and none of the Herters brass develop expansion ring problems. And how is it that, when I run the same test with the same number of mixed commercial brass - they all develop shinny expansion rings after three firings - and most showed problems after two firings as in the photos below?
What are reality-deniers thinking is going one here? Were all four of my test guns functioning properly while I shot the Herters brass reloads and then the headspacing on all four test guns went South right after - just when I switched to mixed commercial brass? Geeeezzz ...
Here, once again, are the links to photos after a total of just two firings. (click on the blue links).
All Brass together, Herters Brass 1, Herters Brass 2, Mixed Brass 1, Mixed Brass 2
I believe that what's really happening is that, on firing, the Herters brass TEMPORARILY stretches lengthwise (axially) - to briefly close the tiny necessary headspacing gap and then it springs back again - as it is supposed to. This almost instantaneous spring back restores most of that tiny but necessary gap - without opening-up an internal wound at the expansion ring area. It does this because it has enough internal web to spread the temporary stretching forces over a greater area.
The mixed commercial brass is all "fruit of the same tree" - having been produced cheaply without enough brass in the area where the web should be. When it is stretched, the case gives-up internally at one point and doesn't fully rebound to restore the small, but necessary headspace gap. The next firing further stresses this already-damaged area. You know the rest of the story.
Again the good news is that - as Rowan and Bloke on the Range say (at 6 minutes and 52 seconds) "unless you're getting light primer strikes or primers backing-out, there's nothing wrong with your gun" (Click on LINK).
Because you are a dumbass and FL size your 303 brass.
Below a rubber O-ring is fitted around the case rim that holds the case against the bolt face. This prevents the base of the case from stretching in the base web area.<snip>
Below its simple with your Enfield rifle as long as you don't exceed the speed of light.
Still stuck on the web thing... Given that the incipient separation occurs ahead of the web, one could easily argue that provision of a web solves one problem and creates another. Btw - Have you measured the OD of a virgin Herters case at the base and compared it to a fired case, or a virgin North American case?
The old Herter's company was an interesting one. Some of their advertising bordered on snake oil purple prose. I suspect that the cases that are working so well for you were sourced in Scandinavia, probably decades ago. You are fortunate to have a good supply of them. Getting more would be catch as catch can.
It is my understanding that some of the best .303 ammunition - and brass - was that made by Defense Industries (DI headstamp, CIL) during WW2.