Vipers -- Not 100% Invulnerable

I never had any trouble on my buc doing

Barrage -> corkscrew -> Double upper -> Barrage -> Corkscrew...

I don't seem to get hit at all when I do this 0.o

Or did I just get extremely lucky until level 135 (stopped there, haven't trained him since).

This is 100% invincibility, but it's deathly slow training since you're only killing like 1 mob.

I've always had trouble doing a backspin--> DS. That's the point where i always get hit unless i rapid press my keyboard buttons to try and beat the lag.