Thanks for this very detailed explanation Rob. It goes further than I expected but is all the better for it. I would be very surprised if any problems were caused by publishing a charge pressure ... I am sure it is available elsewhere on BBS threads ..... but I thought it would complete the picture of an excellent thread. I always find it interesting that the HW90 uses a lower pressure but have not really investigated why ... are cylinder sizes different?
Overpressurising can be a real issue as I know from experience. Many years ago I bought a cosmetically perfect .177 HE at auction for a very good price. Full of anticipation when I got home, I chono'd it ... a measly 5ft lbs with a very hard cocking action. I had no experience of the Theoben gas ram so did not know the correct cocking effort but was surprised it was so hard. Similarly I had never serviced a ram so took it to Theoben. The diagnosis was over pressurising and a burnt out piston head. In this case I think it may have not been possible to pump it up over 12. My auction buy was still good value but it was a salutory experience.
So ... thank you,
Cheers, Phil