Quick follow-up with some results...
I was looking for a cost-effective bulk lube (i.e. something that could be sprayed) that would work for tough sizing requirements where lanolin & alcohol lube (e.g. Dillon or home made) was failing and leading to multiple stuck cases.
One suggestion I'd seen elsewhere was
Lee lube diluted with alcohol to make it sprayable. I ordered some of this (at about £5.00) to try out. I tried a 1:3 then 1:4 mix, but the lube didn't dissolve despite lots of effort and warmth, and it left a lumpy 'curdled' mixture that I thought would clog the sprayer. However, it did spray, and once dry (leaving a 'milky' residue on the surface) the lube worked brilliantly; the sizing that defeated lanolin + alcohol proved no obstacle. The lube is apparently wax based, and the lube of choice for smaller volumes would, of course, be Imperial sizing wax. Perhaps a stronger lanolin mix might have worked, but others certainly seem to have reached the limits of lanolin lube in demanding circumstances.
As it turned out, I found that I actually didn't need to squeeze the base down as much as I thought for this chamber - the base did need moderately tight sizing, but there was also an issue at the other end which was easily overcome; I can continue with lanolin lube, but if ever the need arises I now know I have an alternative for more demanding scenarios.
Hope this might be useful to others.
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