To form rings I bend 6mm round bar round a piece of 2" dia bar, put the bar vertical in the vice, just put enough of your round bar between the former bar and vice jaw and begin bending around the part of the former that is sticking up.
You can slide a bit of tube over your bar to exert more pressure if required, I usually go round about 6 times and then run the slitter down...result..6 rings.