Hunter cannon would kill a minifig easily in one shot, correct? So let's say it's a 2d6 gun, which is very strong in Brikwars standards.
Using an average of 4 for those d6's, that makes it 48 damage.
Now we use the stats that I proposed with Master Chief having 6 Hit Points and a d10 averaging at a higher 5, and we get 54.
There, Master Chief survives.
Hit Points (6)
Mjolnir Power Armor (+1d6 Armor, +2 CP, -2 Move)
Hero Without Ego (+5 CP)
There. If anything, he's on the cheap side, but I think he's close enough.