Since the introduction of the G5Montecs, I've always been a fan of the solid piece broadhead that is resharpenable. I'm currently shooting the new NAP Hellrazors and love them. They are scary sharp when taken straight out of the pack and fly true. The other day I harvested a deer with the Hellrazors and now need to resharpen the broadhead. My question I'm asking is what sharpening stone should I invest in.I prefer the flat stone if possible.

Thanks