For classes with instant high-damage spells or multi big hit spells (Warlock Havoc and Spriests Mind blast + SW D is what I've tested this with) you can kill multiple weapons on the Siegecrafter Blackfuse Conveyor Belts. I'll get an SS in the next hour when my LFR queues up. (Have tested N/Flex and LFR, Not heroic though) for some this could be useless because in normal/heroic it requires a pretty substantial amount of DPS to pull off,
Step 1 : Get two weapons to "kill range" (with a casted spell + instant spell combo, first weapon gets the casted spell, (i.e Mind Blast) and the 2nd weapon gets an execute/high damage nuke that is INSTANT! Projectiles will likely not work(i.e Shadow Word Death)
Step 2: Use casted spell on one weapon, and an instant nuke on the other simultaneously
Both weapons should drop to 1 hp and die before reaching the end.
I've had 100% success doing this as destruction and a 80+% success doing this as a shadow priest.
(Couldn't find similar post regarding this, if one is found I will report to delete the thread)
Note; I used Grimoire of Sacrifice as a Destro Lock, It may have something to do with the Chaos Bolt DoT that caused my success.