The cylinder (~.5 kg) I purchased with my corny keg has finally run out, and I managed to source a new pub gas cylinder (6.35KG) from a local aquarium suppliers. I disconnected the regulator from the smaller grey bottle and reattached firmly to the larger bottle. Everything seemed firmly connected, so I turned on the tap on top of the cylinder, and I heard hissing gas coming from the seal between the cylinder thread and the regulator nut.
the regulator I have is pictured here.
Here is a picture of the empty cylinder regulator connection for comparison
the full cylinder connection is here...
Are all regulators made equal? Am I missing something obvious ?
I can take more pictures if needed.
Thanks in advance for any help given

newelley