[hickgun]

In theory a 300 bar bottle will give you considerably more fills if you apply the perfect gas laws i.e. a 300 bar 10 litre bottle should contain 3000litres of air.

However, the perfect gas laws start to break down around 220-230 bar so you don't get that full 3000 litres.

However, that's all academic, for an airgunner who doesn't want to go to the dive shop too often a 300 bar cylinder is probably a better bet if you can get it filled to 300 bar. Some shops can't do gas to that pressure and even if they can, it can be a long, slow process to get the pressure up and then, when it cools back down, you still won't have 300 bar.