Was on 2nd shot, took the trait on Aram and it become active. Was still firing every 4th shot. UI was still 4th shot. Check back on traits multiple times and was definately chosen. I took Veteren Marksman, Sustaining Rounds, Unstable Compound, Raynors’s Raider, Give Me More, Bounty Hunter and Sergeant pepper
The way Sergeant Pepper works is slightly misleading. It doesn’t actually directly reduce the number of basic attacks needed to proc his trait, it just automatically fills in one of the bullets after his trait is used. If you take Sergeant Pepper while needing four shots, you will need to shoot four times to get the benefit the first time.
Also, the UI doesn’t change. It still looks like you need four shots, although one of the bullets will always be filled.