Roll pin punches are have a small round protrusion at its tip which serves to nestle it into the hollow space of the roll pin. It helps to stabilize the punch into the roll pin when you either drive in or drive out the roll pin. You can use regular punches (and I have in a pinch), but if you're a mite bit off, you can start to split the seam open.
Use the right tools for the job. Buy a set of roll pin punches. BTW, for the M16 you'll need the 1/16" one to insert the roll pin on the bolt release mechanism and gas tube. Don't recall whether you need a larger one elsewhere on the M16/AR-15.