I have a motorized bead roller and work with 16-18ga. The harborfrieght etc can't get the job done, i have seen people brace them up. The real problem is that the bead roll proportions are all wrong. I have even made my own dies to experement. The best thing i have found to do a firewall (other than with a nice big press) is by hand with a self made die and receiver. take a couple pieces of steel (1/8 X 1 strap) and tack them to a plate with a 3/4 or 1" gap (however wide you want your 'bead') the die is a solid chunk of steel - so's you can pound on it, about 6" tall like a big punch - the die part has to be the width of the gap you created with the strapping - less an 1/8th or so and most important! it has to have wings on either side that extend to the outside edge of the steel strapping, the wings are what makes the 'break' in the metal. The die cannot be very long - maybe an inch long. Set your metal on top of the receiver plate and beat the hell out of it with the die.
I make them as needed and don't have one right now, if you want to try it but can't vision what i am trying to explain shoot me a pm and i'll whip one up and make an example seam ok?