This is certainly another material that can work very well with the "flap" disc on a 4" grinder. Grits 60 & 120 would be the best combination for most sorts of cork.
One of the major differences of the cork used in bottles in the purity/compression of the raw material itself, there is, some corks are made of very fine cork pieces, where only select corks are used, and then the most common bottle corks where the cork is a little courser and all varieties of corks and parts of the cork are use. These are not normally as "compressed" as the previous ones I mention.
The final results can be quite different from the various bottle cork producers, all will have its own characteristics but "heavier" colours will be achieved on the less compressed and all corks used on its production.
The "Flap" disc system will successfully turn any cork into a pen barrel without any risks of a catch and blowout, right to the stage of the hand sanding steps. Shaping with the 60 grit and finish with 120 grit will void excess heat on the cork and will leave a good finish for the hand sanding starting from 150-180 grits, up to whatever you like, normally 400 to 600 grits.
Most will already know what this "system" is and many have already tried it with great success, as I'm told so, for those not sure of what I'm talking about, bellow are the pics I always associate with the subject.
Good luck...!:biggrin:
Cheers
George