The other day i was doing solo master lost sector, had heavy finder on, and for some reason the floor was littered in green bricks , but hardly any purple ones. Did not run special ammo finders.

They want you to use a primary ammo exotic to trigger ammo drops, so you aren’t using the stronger energy and power exotics so much. If you’re using legendaries, make sure they are crafted or enhanced, so you can use the ammo finder mods on the weapon. Legendaries need the double boost, but still not as effective as the exotic. Just wait until the update, special ammo finder will now be taking up one of the limited armor stats instead of a mod slot. So now we will have to choose between abilities and ammo, instead of getting both. Isn’t that so much better?

I've noticed sparce drops from time to time, and I've had a degree of success by using special weapons more often (when trying to get heavy ammo). This is based upon an old restriction in the game (maybe even d1, don't know how relieved it is right now.... but old habbits) where there is only so much stuff that can drop on a map at any one time... so if the floor is littered with special bricks do yourself a favour and pick up all those bricks.... once it's clear you might start seeing improvements.

I find rotating through weapons tends to stir up some drops, almost as if juggler is still a thing under the skin........

If you have finders mods on you get the increase when you use kinetic weapon rather than a special or heavy weapon, so if you need ammo use primary and will have higher drop rate on kills.