A player by the name of Darkdemon8910, Whom was participating in #TheHunt2017, recently discovered that the Skullmasher does indeed drop from Rakkanoth in the "Sir Hammerlock's Big Game Hunt" DLC. He claimed to have seen it drop several times from the boss while farming him via dashboarding. Joltzdude also made a video on this and has gotten it to drop for himself, further proving this to be real. This is good news for anyone struggling to farm Son of Mothrakk as he is very difficult to farm and his loot has a high probability of glitching through the floor. Rakkanoth also makes sense to drop the sniper as he also shares Mothrakk's skin drops as well. But be advised, Rakkanoth does not respawn so make sure to dashboard or Alt+F4 if he doesn't drop it. So to summarize, Rakkanoth also drops the Skullmasher so you dont have to farm Son of Mothrakk. Happy Hunting.