Rich yes its frustrating not having the pressures in the User Handbook. I suppose the Army like to keep that info separately in the Servicing Schedule along with POLs as these things may change from time to time & reprinting a publication of 2 or 3 pages can be done more easily. Although the Commer book being a civilian publication, has all the info together.
Here is a bit info on the FV1622 in service
http://hmvf.co.uk/pdf/MISSILE%20TESTING%20HUMBER.pdf