I cant emphasise how dangerous this can be, your dealing with pressures in excess of oxy acetalene bottles and not tested!
Swat up on what you are doing, if its not you its others around.
Its not so much the rated tube, its the plugs in the ends which are the most vulnerable usually.
80 though wall i wouldnt want to put 200 bar in whether or not its passed a 300 bar test.
Mind one well known manufacturer uses 27.3mm bore with M 1.25 pitch
Blows at 245 bar thats about 60 thou wall!
30mm o/d with 2.5 thick wall hydraulic tube is pushing it for 350 bar with pinned ends. Yet going 20 thou thinner and 1/16" larger dia adds to weakness, dont assume for one minute that will hold 4500psi. These are nothing less than a potential bomb and have seen for decades what you boys do over there. Cap head screws should take the load on the head not the thread.
Cant quite see but think thats done right on the 1" o/d tube, heads going through the tube and in to the end plugs, the thread just stops them dropping out when no pressure in. Unlike a certain manufacturer your way and predecessor using mush head screws on top of o/d of tube with 3/16" screws having the shear on end plugs.
To pin the cylinder on 1 1/4" stainless G316S11 X 1/8" thick wall i used M5 cap heads 17 years ago. Took it up to 6300 psi before 1/8"BSP off the shelf thread sheared. Th end plugs moved as well stressing the materials also stainless steel.
I wont remind you of the numerous failings due to incompetant tatters, even if Ginb didnt make that cylinder, he messed with it and should have slung it back if he knew what he was doing! Carreers another totally dangerous as is any CO2 pressure vessel operating at more than rated value ie air at 200bar.