One article of faith among those veddy-veddy gentlemanly tweedy types of yore who shot long-range matches with the .303 #4 Mk 1/2, is that the ammunition and the chamber must, repeat MUST, be free of oil, grease, or other slickums that might reduce the traction of the tapered case against the chamber. Most such practices are well-based in over a century of target-shooting research with the olde Enfield and its equally-geriatric cartridge.
For a considerable length of time, I've been striving to maintain such conditions in my .303 rifle chambers. The current batch of brass I'm using, upwards of 600 rounds or thereabouts, was all bought new from commercial sources, and has only been fired in one rifle. Most of it has been loaded at least six or more times, and there have been no case failures to date.
Note that I took NO precautions with this brass against the first-firing "stretch" which afflicts cases fired in military .303 chambers. Even without such precautions, the brass life is excellent.
The main reason for this is the fact that I only neck-size the cases, taking pains not to touch the shoulder with the sizing die. A sharply-tapered case like the .303B makes avoiding die contact with the shoulder rather easy.
In my normal routine, brass coming home from the range goes directly into my tumbler, with 1/8"-grind corncob and a shpritz of Turtle Wax "Scratch and Swirl Remover". The cases emerge brilliantly shiny, far brighter than new factory brass, and CLEAN. The question became, how to maintain the pristine state of the brass, and not guck it up with some lube which then would be very difficult to totally remove, and which could harm the rifle's performance through chamber contamination.
It turned out that the answer was simple. For over two years now, I've neck-sized my freshly-tumbled .303 brass with no lube at all. After some thousands of rounds through the sizer, there's still no measurable change in dimensions. The neck-sizing effort is minimal.
I avoided mentioning this until now, because I wanted to have a large number of cases sized in the die before reporting my conclusion: it works. There's no apparent harm to the die from the lack of sizing lube.
Cast-boolit lubes don't seem to migrate onto the cases (and chamber) when fired, at least as long as pressure is high enough for good sealing of the chamber. Cases look just a bit grubbier than they were before firing, but don't seem to have any slippery residues, which "should" mean that the chamber is staying free of lube, too.
Now, if the danged rifle would just SHOOT with cast boolits, I'd be a happy man. I just completed the bedding job on Miz Liz, and hope to report on IMPROVED performance next week.....