It`s a lot more than a powder load. It`s about "pressure" ,squib loads have been known to blow things apart also.
All brass cases no matter the cal. need to be loaded "full" so to speak. That why there are a variety of powder types for reloading. Some will fill the case and some wont. With a seated bullet the powder usualy is to the bullet base. This keeps the powder in contact with the flash hole. Cases less than full need some type of filler material to keep the powder charge at the flash hole when the round is horizontal .