A very easy way to get this is to play Daybreak. The first Blood Juggernaut shows up in round four, at the one minute remaining mark.
Round one: No juggs
Roudn two: No juggs
Round three: One normai Jugg
Round four: One normal Jugg followed by one blood jugg
Round five: Two blood juggs
Round six: Even more blood juggs
Round seven: EVEN MORE blood juggs
Since the make or break level in Daybreak is level five, you should be able to make it through level four with a little practice.
When the blood jugg appears, just repeatedly shoot it in the head, then do the
move to it to instantly kill it when it is kneeling from damage. You can also continue to shoot it in the head for a faster kill.