German to English Tech/Engineering Mechanics / Mech Engineering practice ammunition in cartridge form

I assume that Rastnuten refers to "grooves" but what is a Rastwulz? Googling and researching does not yield anything. I suspect that it could/should read "Rastwulst" but I admit being puzzled.
The full sentence reads as follows:
"Steigt der Druck in der Kammer weiter an, so wird bei einem bestimmten Druck der Rastwulz der Patronenhülse an der Rastnut des Geschosses abgeschert, sodass das Geschoss ausgetrieben wird."
I would not mind getting help with the entire sentence but shall certainly appreciate explanation/translation of
"Rastwulz" from a Fachmann i.e. 'person skilled in the art'.
Thanks in advance and have a happy New Year!