That is a logical explanation of the shortage in ammunition and reloading supplies. The blackpowder shortage is possibly somewhat related, as the smokeless supplies dried up, people shifted to muzzleloading as the next choice. Archery next?
Artillery and naval guns use nitrocellulose based powders for propellant, there is no large military use for black powder that I know of.
the market (populace) is nervous, so people buy more firearms, ammo, and realoding supplies... demand up, supply down, prices up (ususally would smoothe out supply/demand, but firearms are an oddity)... prices rise, people get more nervous ($30 for a box of 9mm?!?!?! what next?!), buy more... demand even higher, supply down... prices even higher... manufacturing is at about 100%, and can't keep up with demand... that leads to shortages and rationing (some stores around here have 2 box limits on ammo)...
i think it's gonna be a while until this settles... (i know here in NH, both SIGARMS and Thompson Center arms are running 24hrs a day, 7 days a week, with 200-300% increases in employees!)
An unintended stimulus package caused by the current administration in Washington,DC!