From the location of the bulge it appears the bullet was not seated or there was an obstruction...that is well forward of where the seated bullet would sit in the barrel. Under normal conditions the pressure would be well on its way down by the time the bullet got that far down the barrel. It's really hard to tell in these cases with limited information.

MTA: Possibly he had a misfire and re-primed without making sure the bullet was still seated firmly on the powder. Elsewhere they have information that this individual was a relative newbie to smokeless (under 100 shots). We'll never know what happened, if he double-charged the gun or otherwise screwed up he'd admit it about as freely as any man would admit to a cop that they were doing 30mph over the speed limit when an accident occurred.