I've seen a fired case like that, the chamber had been machined very badly. The one in the picture looks like the bullet has been seated in a case whose neck had been stretched before the bullet was seated.
Look At the shoulder, it been pushed back into itself a bit by the looks of things.
Could be over zealous seating with a case that's been neck turned too much .
Shoulder profile is not 308 win
no angle, almost looks like a Weatherby secant shoulder
bulge is the neck collapsing
I think that the shoulder has bulged too.
Case may have been filled with something rather incompressible other than powder?
308 boat tail rammed into a 270 brass
Does the die used have the ability to crimp? As it looks like some I made when I was learning how to set my dies up screw the seating adjuster in and die out should prevent it happening again. Then read the dies instructions again.
Bullet seating die screwed down too far and squashed the case, causing the ripple in the neck and rounding of the shoulder. I have a near identical 6.5x55 case that resulted from my first attempt to seat a bullet in that calibre!
A bit more info.
History unknown. Case looks distressed.
Case is headstamped RG 08/80? and a + In a O.
Missile is FMJ diameter measures at 0.300" Primer sealant red.