Interesting, I've been shooting Ackley Improved cases since 1977 and have never had one stick. They are the easiset extracting case designs I've ever used. I once had a pressure excursion in a .375IMP (wrong powder for the case) and the bolt opened normally, however the rear of the case was almost gone - melted. I tilted the rifle up and the case fell from the chamber - I have never seen one stick.

I have had lots of bolts stick on tapered case chambered rounds when developing hot loads, however.