Oooh, this happened to by brother in law’s AR once. I ended up having to disassemble the upper to get the barrel into a proper vice, then slowly drilled the primer out, and used a puller and small slide hammer to pull the bulged casing out. Unfortunately, there was damage to the barrel where it looked like the side of the case neck blew out and the bullet did something bad, there was some burned metal like a small torch eating away the metal. A headspace tool wouldn’t fit in the barrel as a quick check so I used a small camera to inspect. I ended up installing a 16” Colt take off.