Hi steve,i was in the 850 resource forum some time ago,if your 850 was tuned by Roald,i am pretty sure your valve is still flowed and the rifle has Roald's hammer spring in,so most of the work is already done.You can choose the "long" AS to PB adapter if you intend to use a 13ci bottle,this solution become unpractical using a 22-23 ci bottle,in that case the short adapter is the way to go,but you will need to drill holes on the plastic stock to fit the gauge and the fill nipple.In this configuration the most popular working pressure was around 1800psi for a power of around 32FPE.
No oil in HPA systems! Fro safety, no more than 1100-1200 psi.
Just heard from Roald, an 850 reg tank is what i need. said 1100 could cause valve lock.
pretty sure i have the stronger spring since the valve will stick open if i dry fire it...hmmm