Maybe this will help...some pics from a Tutorial of mine (on the subject of Black Nebula) but it shows how I wind my footprint onto a 3/16" mandrel. Once you get it on there and even, you can continue to marver it into something of a longer barrel shape. If you want to make it go "round", marver it into an even wider barrel and add another layer directly down the CENTER of the barrel only. Once it's returned to the flame and heat is give to the center applied layer only, the sides pull in a bit and the center layer starts to even out making the gather go round.
Heat the mandrel thoroughly to glowing; simultaneously heat the tip of your glass rod:
Begin a nice, even, narrow wind as the "footprint":
Add a second layer; melt in:
Use your graphite marver to flatten this footprint a bit as well as true up the sides as necessary:
Very gently marver again to flatten if you wish, or leavel as a "donut".
This method creates a bead that looks like this:
If you want to make a round, slowly and gently flatting this donut shape to spread it out about twice this width, then follow my instructions above about adding another wrap to just the center of the flattened barrel.
Hope this helps you a bit.