Ok thanks for the link.
Found on some french forums that some people have tried (or heard, not clear they dont make full sentences...) that it's the space in the mags the problem too. CoČ is in liquid in the mag, so I understand for those, but GG was pretty sure was in gas form.
Think best thing is to buy 1 mag, tape a sticker on it to identify my (testing mag) and try it myself
-KWC P226 X5
-Ra-Tech WE HK416