The proton cartridges are regulated. There is a main filling chamber which is 200 bar then a small air space before the top that has a spring type regulator. I spoke to Mr Camilleri and he loosely confirmed this, i also have managed to find copies of plans for prototypes and finished model on the internet which show this. Mr Camilleri is a gent and I have the utmost faith in his work of which I'm sure a lot went into making these.
With the co2 however i am now not so sure. So should I weigh them before and after filling and is there a way to confirm that they are 12g before i start? Having a mini co2 cartridge primed to explode due to lack of expansion space sounds bad. Maybe just sticking to room temp may help as its less likely to over fill? I'm wishing i had instructions but nothing came with them.