Thanks Daryl,
the visible pressure line at the web on .30/06 and 270WSM cases here seemed to start about 1/4" from the back of the rim but the 6.5x54's was 3/8".

Your zero-expansion allowance on the solid head in front of the extraction cannelure makes sense to me according to the ancient advice I was given BUT I find it often in fired factory cases (including the belts of magnums) and even 2 thou on the 270WSM, hence my resolve about reloading them. Is it possible because of less-brittle brass that factories are loading to higher pressures than they use to? I noticed tables on the opposition website where some maximum loads nudged 64,000psi. As I noted there, when I was young that would have been a British proof load, though they may have been CUP figures 50 years ago.

Sorry, I must have read too quick and missed your already saying that 'overpansion' of the web area indicated a large chamber.

- Paul