HydroTest of paintball CO2 aluminium tanks

Hi everybody! I had 2 paintball aluminium tanks. 6 and 12 Oz. So I decided to chek them on extremal high pressure. I connect tank to hydrotesting device. 6 oz tank was pressed to 200, then 300 and 400 bar – it do not deform! When I put pressure to zero and measured it diameter – it does’nt changed. Only when I press 470 bar pressure stopped to rise – tank begins to deform. On zero pressure it’s diameter add 0.2 mm. So I throw it to garbage – it’s become dangerous to use.
Then I check 12 oz tank. I press it to 200, then to 300 bar. Then I put pressure to zero – it does’nt deform. So I guess I can use it for 200 bar air.

Discussion with photos and table with measurements You can see on Ukrainian forum: http://airgun.org.ua/forum/viewtopic.php?f=15&t=21377&p=370846#p370846

Excuse for bad English.
Best regards – Gennady