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.