Ak has the right of it. Its a random roll. 1-4 operator, 5-6 cannon.
> You've got the allocation of hits backwards (RB Pg 55, 2nd para under 'Shooting').
The TFC is the one "must have" unit in all my lists now. There is no better value HS choice for C:SM IMHO. I put it and/or the TM in a ruin and have the techmarine bolster the ruin. Now the unit gets a 3+ cover save, and/or the TM his 2+ armor save. Four blast templates with 3 munitions choices is fantastic, even for lousy rollers like me
. One of the few units that can wipe out an entire infantry unit with some good rolls. Add the 60" range and it's a keeper for me.
Yes, it's a "glass cannon", but since I usually also have Preds and/or Vindis and maybe a dread or two, it isn't usually fired at until it's already earned it's points back. Especially true in my club as I'm the only one who seems to play it, so unfamiliar opponents tend to ignore it until after they've felt the pain.
On a related note, one especially cheesy variant is to get the LR Achilles which has the TFC, put 5 scouts in it, park it on an objective and blast away while shouting "come to papa!".