Get a surface use only bottle so tested every 5 years rather than annually. I don't use pcps much but have a 12 litre 232 bar faber steel cylinder that does just fine. 1 fill lasts me 5 years I found id have to travel quite a way to find someone with a 300bar compressor so happy with large volume 232bar. Ex diving cylinders will of had a harder life than the airgun cylinders so I'd look for one of them personally.