Bulged cases are usually caused by the sizing die squeezing the case down too far in diameter for the bullet used. Measure the case mouth inner diameter after the case has been sized, and after the case mouth has been flared. It only needs to be .001 to .002 under bullet diameter for a tight bullet fit.
If the case mouth inner diameter is less than .001 -.002 inch under bullet diameter, the bullet will push out more on the weakest side of the case as it is seated. This is because cases are rarely the same thickness and/or hardness all the way around the circumference of the case mouth. The fix is an oversized sizing die, or smaller bullet diameter.
Bulged cases are cosmetic only and pose no danger in shooting.