Evening all, and a happy new year

Long story so I will shorten.
After a long lay up, my S400 was leaking when refilled.
It would leak down to about 90 bar and stop, but wouldn't hold higher.

Over the break I have replaced the seal in the fill valve that appeared to be leaking, and also replaced the firing valve for good measure.
However, I now need to get a charge in from empty ! (Yes, the gun is cocked !)

I only have a 12L 300 Bar tank these days, and that appears to have one of these slow fill or restricted valve heads on it.
Consequently I cant get enough of an initial blast to overcome the firing valve, and it just vents from the barrel.
I have had this issue before with this tank, but back then I had a second 232 tank that I was able to use.

We are currently in self-isolation, so I can't go anywhere to borrow a different tank.
Its not the end of the world, but would just be interested to hear if other people have come across this, and any tricks to possibly try and get round it ?

Thanks,
Andy