The use of a roll crimp in this case certainly exacerbated the problem. The roll crimp shell has a longer "Loaded" length than a fold crimp one having the same fired length. If in the case of this gun it had an extremely short cone the loaded shell may well have actually been pushed into the cone upon loading. This would in effect give a much stronger crimp strength, delaying its opening which can give drastically increased pressure.
The firing of a longer shell than the chamber length is dependent on there being clearance between the end of the loaded shell & end of chamber. It is further dependent on the end of the shell only lapping into a cone of normal length & not a very short cone which would allow the shell to reach either into or almost to the bore itself.
