You have obviously never reloaded S&B 303 brass.
We had a competition at the club to see who could get the most reloads out of it - the record was 3 (a total of 4 firings) the majority failed on firing the 1st reload.
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If the powder still smells "sweet" an flows freely when decanting from the cases, it is probably OK. Any hint of "acidic / tangy smell or "clumping" of the granules usually means it is "off"
If in doubt, decant the propellant, (it makes a handy fertilizer in the garden), remove the BOXER primers with one of the dedicated "de-prime only" tools. The original bullets and cases can be tarted up in the rotary yumbler and put back to good use with fresh primers and powder.
If you ere contemplating doing such salvage on BERDAN-primed ammo, it is a bit more complicated. Before you even startrt, confirm your source of replacement primers.
With that sort of thinking you'd need to keep a box full of bolt heads in your range bag and fit a different one for each brand / lot that you use.
The problem of minimising your bolt head using 'thin rims' is that when you do use some mil-spec ammo you won't be able to close the bolt.
Still wont stop the case head separation, the cases are undersized and or made with a poor quality brass.
Togor some of us have been dealing with this problem for 40 years or longer. It is not a new issue. Reloading the 303 and its derivatives has different issues to any other case i know and i reload for more than a few in both camps rimmed rear lockers and rimless front and rear lockers.
Might have thought the :) would have signalled the light humor.
Maybe Enfields aren't funny?
I look forward to shooting these, when the weather warms up. See what they can do.