I remember that I noticed the little nub pushing the BB from the magazine into the hop-up chamber was slightly longer on my V2 bolt when I first had it. Now that the season is almost over, I'm gonna do some more testing to know why my V2 bolt had been such a pain, I ran my V1 all summer instead.
EDIT: Had some spare time, and a Madbull 6.01mm x 509mm laying around since 6 months, decided I could mod it to fit into the KJW hop-up system

Now I just gotta find myself a 150mm silencer to hide this hehe !!