Critically conditioned: Charge Rifle challenge

I was just able to finish it...here is what I found:

1) shoot the charge rifle at the RED SPOTS on the Titans...that is almost a guranteed crit

2) NPC Titans are a lot easier to hit as they don't hop around

3) when using the AMPED card for the charge rifle, use it to Rodeo Titans...much higher chance to CRIT

4) don't forget, it is a general crit against any target...use it on the MARVINS