Unlike Volatile Rounds and most other effects that care about a weapon's element, a weapon that has become Strand through the Osmosis perk does not gain the benefits of Unraveling Rounds. I'd feel like I was being patronizing if I actually wrote out step by step instructions for reproducing this, just take any Osmosis weapon and any source of Unraveling Rounds and watch as they don't work together. If Volatile Rounds also didn't function with Osmosis I'd probably just be disappointed, but the fact that the two nearly identical buffs apply inconsistently makes it clear that something's not working as intended.