User blog:Brothertim/FMJ in SMG: tips?

On my almighty quest to achieve mastery (unlock all attachments) for every single weapon, I will be starting the SMGs very soon. I've already run through all the assault rifles, with the exception of the AK-47.

My questions are:

1. How difficult will it be to unlock extended mags on each SMG? (I assume they all have shitty penetration)

2. What is the best game type to do this? (hardcore probably, but I like core more)