I've never held with the notion that the expander button "pulls" and stretches the case on being withdrawn on the return stroke, though I've not thought about it actually shortening it. Sizing seems to produce elongation in proportion with the extent to which the case diameter has been increased in the chamber compared with the dimensions of the sizing die itself.
I've been working three thousand cases with head stamps (virtually all HXP) from the early '60s to the late '70s. All have been fired once (three point crimped primers still in place) most probably in the Hellenic Army's M1919 Browning machine guns. Having sized a few hundred thus far, I can safely say that at least one of those guns has an enormous chamber.
Unclenick: our postings passed each other in the 'net. I've encountered no trouble in priming these cases without
making any attempt at removing the crimp. I like when things like that happen.
I've had, mebbe, 6 more stuck cases, all of which I've removed in about three minutes. The RCBS lube appears to reduce the friction of sizing marginally better than the wax, but I've experienced sticks with both. I think they're more likely when I haven't done a complete lube job.
Both of the sizing dies I've been using are standard SAAMI spec., or at least there's no indication of their being SB.
The occurrence of stuck cases is diminishing as the number of cases sized accumulates. This is probably the result of the inside of the die being burnished by repeated sizing cycles.
I've ordered or scrounged some of the different lubes that folks have mentioned and will be giving them a test drive shortly.
Unclenick: it looks like our posts "passed each other in the mail". I'm finding that I have no difficulty inserting primers without
making any attempt at removing/altering the crimp. I like that in a case.