Castrol (& other) grease comes in a plastic pot with a mega washer in the top. The mega washer has a 12mm diameter hole. Simply place the open great gun over the hole and push down. In seconds the grease gun is full. A slide to one side to finish off the fill and a minimal wipe over required before re-fitting the top of the gun. All you need to do then, with a pistol type gun, is to bleed out the air. Simples.
