Currently in Extremes and 4th floor Savages in a tier, the loot that will drop upon clearing will include a weapon coffer and a random job-specific weapon. I suggest instead to make it so that it is just 2 weapon coffers. With each new expansion where they add new jobs, the chances of a random job-specific weapon dropping for the job you're currently on gets lower. There's also the rare scenario with certain parties where no one plays the job for the random job-specific weapon that drops.

Coffers have the item description of "Cannot be opened in instanced areas such as dungeons, PvP areas, or raids." and because you can't have 2 of the same exact weapon coffer in your inventory at a time, there is no need to worry about a single person winning both weapon coffers. However, in a scenario such as in a static where you'd want to give 1 person both weapon coffers(because for some reason no one else wants them), I also suggest that this rule can be bypassed. For example, lootmaster bypasses the can't have 2 of the exact same weapon coffer rule. Or if no one else rolls on the weapon coffers this also bypasses that rule.