maddman spring kit.
That might work.
But the real problem is that you are using an LP valve designed for around 400psi or less input..and a 12 gram outputs about 800PSI depending on the temperature.
What you really want to do is get a normal HP valve from PPS or find an old Sniper valve. The PPS HP LT valve will the be your best bet by a long shot for unregulated CO2.
You could also use your 12 gram co2 and run it into your high pressure regulator that should work well too, if the grease in the HPR doesn't turn to bubblegum in cold temperatures.
"I'll see it when I believe it"
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