If your 12L had 300 in it you would not have 300 in your 7ltr after decanting, what pressure was in the 7 ltr before decanting? if you know this some simple math will tell you the start pressure in the 12ltr.
I had my 12ltr 300 bottle filled at Go Dive in Derby last week and watched their gauge and my bottle gauge go all the way to 300 as they filled it. It will of course drop a bit due to the temp rise in the bottle dissipating. The emptier they are when you take them for filling the greater the temp rise and the greater the drop will be as the temp normalises. I am certainly not getting short changed but physics plays a part in how much pressure remains.
HFT, for people with only 2 buttucks!
VooDoo TwoTwo The next chapter.