Using basic mandrels is fine but I like the type that has the sharp tips to place the metal beads or copper tube on.
I find that the sharp tip makes it easier to put the metal bead or tube on to work with
Thompson has great Bead Holders with tips but I am in a rush and want to have for my classes
I made some home made ones last night using 5/32 copper tube (12" long) and some 5/32 bead reamer ends
Was extremely easy and when finished worked great

5/32 coper tubing - 12" long (I like long handles)

the 5/32 bead reamer end fits nicely into the hollow 5/32 tube -

I put in about 1/4" of the end of the reamer

then I used my larger cutters and crimped it down to the end - be careful to slightly crimp just below end so that when you push on it wont push the reamer down further

nice long handle

all made up for my classes
took all of about 10 minutes to make all 8
Typically you would use old reamers but in this case I needed some fast so I am using my new ones -
I figure approx cost is 3.50 and I could take another .50 off if I only had 6" handles