This has come up and I have a curiosity on it regardless not to mention with the 303 Rimmed you wind up like a belted magnum with two different players involved in the chamber as it were (probably not well said but)

Was the purpose of the 4 heads on the latter SMLE to tune to the original manufacturing new gun (tolerance vary that much?)

Of was it a field issue?

I have read the rim thickness variance issues of WWI and if they varied that much, it would been to not matter (at least in combat and a rifle with limited life).

Happy for a good reference, did a lot of searching and came up with nothing on that specific area.
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