Thread: Time for the bin?

As @Flyblown stated I too would say that there was one or two pieces of cotton off of a cleaning patch lodged in the neck area of your chamber.
I had the same thing happen with a new Steyr .223 rifle with the very first shot after cleaning the factory grease out of the barrel. On inspecting the fired case there was a 30mm long groove up the side of the case. Looking in the chamber I could see a single thread of cotton. Once removed there were no more grooves. The next time I fired that case the groove fire formed out.