Thanks for the help on this folks, I have got some Proton x2 which are just air and they are sold as being able to hold 200 bar which i think is higher than the Brocock. I thought i would try the Rap4 ones as I have had there stuff before and love their 43cal pistols. I spoke to them and they said co2 was best but air is ok as long as the pressure was around 850psi. My plan was to use these for co2 and the proton for air. I will make up an adaptor for my drulov bulk fill connector and let you know how it goes.