I had 2 x5's. 1 early one mentioned here and one made at the end of 2018. Both bulged cases with the combination of powder and cases I was using.
If I used a slower powder OR different cases they didn't bulge. In the end I was running a 10lb spring in the newer gun, it couldn't fire out of battery with the upgraded drop safety work and ran well apart from the odd case bulge (it bulged with the factory springs too). A tiny bit of slide movement would disengage the trigger. The earlier gun could fire with the slide moved a lot futher back but not entirely out of lockup.
I sold both x5's and am now enjoying the pleasures of full case support in 2011's again.
edit: the cases that bulged or blew out were PPU, Tulammo and the very odd CBC. PPU bulged every time, even genuine once fired brass, Tulammo blew out and the odd CBC one would have been a super old case. Quite entertaining shooting a mag full of PPU and watching peoples reactions as they pick up your brass.