Yesterday was phenomenal, I got my first Gjallarhorn from a Nightfall. This (might) be why: While playing yesterday, I received the grimoire for Rocket Launchers kills III which is after reaching a total of 2500 kills with rocket launchers, while we were raiding on Crota Normal mode. After completing the run, i got: 1- Hunger of Crota Rocket Launcher 2- Dragon's Breath Rocket Launcher Both on crota checkpoint within the same run. Then after that i did a nightfall, i only used the Truth rocket launcher since there's void burn, with heavy use of heavy ammo synthesis and I died A LOT. I think about 10-15 times dead. I even killed myself on purpose a few times (for making a worst death record). Aaaand Voilà! My first Gjallarhorn. That being said, i think getting that grimoire card has really affected the Gjallarhorn loot drop. Hope it helps! :)