"IF" the crimp did not open at all you would of course have a closed cell pressure which would be astronomical. Any increase in resistance to the crimp opening over normal will increase the pressure. The question here however is was the hull itself just weak & broke easier than opening the crimp. If this be the case there was likely no increase of pressure.
I find that No Change in velocity from an as new shell with firm crimp to one ready to fail a Bit Hard to Swallow.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra