Frenchman,
Take a block of wood that you can clamp in your vise and install a dowel in it that has the same diameter as your ramrod.
Find some washers that have a hole large enough that your ramrod pipe can go inside. Select washers that are the thickness of the spacing you want for your rings.
Plop a washer onto the block with the dowel through the hole. Stick the ramrod pipe over the dowel so it fits into the hole of the washer. Now take your 3-corner file and hold it against the washer while you file your first ring. When that ring is done add a washer and file the second ring, etc., etc.
A nice ramrod pipe can be made up in 15 to 20 minutes with nice evenly spaced, uniform rings on the ends.
That's how I did the rings on the pipe pictured above.
Best Regards,
John Cholin