What is it like being a 13B cannon crewmember?

The FA often takes on other roles outside cannons based on their relationship within a BCT. So the answer is that there is the possibility, but not often. The current SMA trainer his Bn to go into the fight in an infantry role. If they are general support Artillery they can take on other support missions as well depending on the mission requirements.

When I was in Iraq my mos was 13B, but you do what is needed, I was convoy security and route clearance, love my gun bunnies, but wouldn't have changed it, we went nuts just sitting in the fob

In COIN, everyone that goes outside the wire becomes a combatant. During current operations in Iraq 13B are/were set up in fire bases. It all depends on what type of operation you would be deployed to.