Gunblade should NOT stop Katarinas ultimate
When you're ulting as
and you use
it will stop your ultimate completely.
I contacted the riot support team and they said > activated items cancels most channels for all champions. But sometimes abilities are modified if the developers feel like the champion really needs it.
and I feel like katarinas ultimate should not stop if she uses gunblade. Gunblade can slow enemies down and if you can slow the enemy down while you're ulting it can do loads of damage on that single target.