Another idea ... very simple but works:
Rifle cylinder clamps to hold the cylinder in a vice (or similar) while you mess about with other bits e.g rebuilding a trigger mech or fitting a BSA sloping end block.
All you need is a short (3" - 4") length of plastic 2" waste pipe and some rubber sheet (rubber belting 3mm thick is perfect). Cut waste pipe in half down its length. Cut two bits of rubber sheet each big enough to fit inside the 'half' pipes and glue the sheet in place ... contact adhesive or similar. Clamp / tie the pipe and rubber sheet around another bit of pipe to keep rubber sheet i place while glue dries. Perfect. I have used my clamp protectors for years and they have not failed yet.
As an extension, if you make another set or sets using narrower plastic pipe you can make perfect grips for other round section parts that you need to grip firmly e.g. by molegrips or water pump pliers without marking the item. If using mole grips I use the grips that have curved faces. For the plastic pipe I have used bits from defunct solar powered garden lights to great effect. I guess hose pipe would do but I think the plastic pipe would give better grip and prevent the mole grips from digging into the rubber lining.
Cheers, Phil