Sandia National Lab was able to replicate the explosion. The key variables were the individual powder bags and how they were rammed into the barrel.
See this training film from 1955: https://www.youtube.com/watch?v=0OmOQs0ziSUThe bags
Each powder bag was approximately 18 inches long and 18 inches in diameter. The bag itself was made of silk, because it burned completely with minimal residue. Inside the bags, the actual powder was in little cylindrical finger-sized pellets. Hundreds of these pellets were stacked neatly in the bags in tier on top of tier. Ideally, each bag would have an identical number of pellets - Indeed each one had the same number of tiers and the same number of pellets per tier. However, due to slight variations in the manufacture of the pellets, two bags with the same number of pellets might weigh slightly different amounts. Since an identical weight of powder was required for optimum performance, every bag was brought up to a standard weight by adding extra pellets to the top of the bag. That is, as the cylindrical bag sat upright, the extra pellets were placed on their side on the top tier, then the bag was sealed.
As you can surmise from the training film at 6:30 - 6:45, when the bags are horizontal on the loading tray, the extra pellets on the top tier of one bag will be pressed-up against the flat bottom tier of the bag in front of it. When the bags are rammed, the extra pellets are compressed. Compression generates heat. If there are a lot of extra pellets, then the pressure on each individual pellet is less. If there are just a few pellets, then the pressure - and heating - on each pellet is increased.Ramming the bags
Note in the training film at 6:20, the projectile is rammed at high-speed
to engage the copper seating ring into the rifle grooves in the barrel. Then the bags are rammed slowly
into the breach. This is the proper procedure and was used safely for decades. However, in the aftermath of the Iowa explosion, the ramming lever was found in the fast-position. Sandia Labs found that if a powder bag with few
extra pellets was rammed at high-speed
, the compression could generate enough heat to ignite the pellets - and the rest of the bags. They were thus able to recreate the spontaneous ignition that occurred aboard Iowa.
Mind you, there is a whole lot more to the story, and the Wikipedia page
gives a damning indictment against the command climate aboard the Iowa before the explosion and the botched investigations and cover-ups that followed. As a former Navy professional, I find the conduct of the men involved nauseating.
Just because it's stupid, futile and doomed to failure, that doesn't mean some officer won't try it.
-- R. Rather