That Bubba guy sure got around doing his stuff! I am thinking the pentagon shape does not go all the way through and only catches on the outside. Maybe the rest of the shaft is round?
There has been some discussion on how available and cheep Krag parts are today. Movieman evidentially has a large hoard of new (unused) bolts and other parts. A temporary fix will get you going for now and a new or used part for looks later, might be a plan.