All that makes sense - compressed load affecting powder ignition resulting in very low speed load that caused the projectile to bounce of an elephant (I've experienced ignition issues and fail to ignite when working up cast projectile loads with too slow a powder). I don't think the term the powder "coagulated" is correct. Maybe the problem was a combined issue of compression + heat (high ambient temperatures)?
And maybe coagulation refers to the appearance of any unburnt powder afterwards. When I had the ignition problems in the early days of my cast load experiments, the black deterrent coating on the powder was blown/burnt off exposing the yellow nitrocellulose, and the powder would clump together (partially melted?) but you cause squeeze it apart again using finger pressure. It was really weird - the primer pressure alone was enough to drive the lead projectile into the start of the rifling (and hard to remove) but not ignite the powder of even blow the cotton ball wad on top of the powder out of the case. If someone had told me this could happen I wouldn't have believed them, but I saw it first hand. Mind you not all the loads did this - most fired or hang fired, and the stuck projectile ended my session at the range for the day.
