This is from the Facebook John Bowkett Fanpage and may be of use to some owners.


Here's some info on how to use the buddy bottle on a sf spitfire

The unique internal straight line valving in the Spitfire dates back to one of my 1980s designs. On Facebook there is a photo of a prototype complete with a slightly different anti-bounce mechanism that I made around 1990 while I was associated with Titan Developments. The production Spitfire was equipped with my S10 anti-bounce device but slightly modified. I will see if I can find the photo.
The Spitfire went into production in 2000. The idea was to use S10 buddy bottles to top up the rifle. It would be a companion to the flagship but at the other end of the price scale using many components from the production springers but with S10 type barrel/rifling. The Spitfire working pressure is only 1900psi (approx. 130 bars). The buddy bottle is screwed directly into the socket in front of the trigger. No connectors or charging gear is required. The combined shot indicator/pressure relief valve cuts in when that pressure is reached. You cannot overfill the gun. The reservoir volume is small (approx. 50cc) so 2 or 3 full fills can be had from a buddy bottle.
However, the secret of the Spitfires practicality is to be found in its shot indicator. The short 10” barrel carbine will give 25-30 shots per full fill and the 15” barrel rifle another ten or so. The procedure is as follows. Set a target at the maximum range you would use the rifle at - say 45 yards (40M). Give the rifle a full fill until the bleed valve cuts in at 2300psi. It will then slowly fizz down to 1900psi (130 bars) which is the maximum working pressure for the valving. At this point the post of the shot indicator will be at its uppermost limit. The post is in the middle of the pressure relief valve. Start shooting until your point of impact starts to drop on target. Note the position of the post at this stage. It has horizontal lines to help. As long as the post is above this level your shots will be constant. Topping up can be whenever you want. The 200cc bottle is small enough to be portable and there is no charging gear. After a couple of fills the bleed valve will not hiss because its pressure has dropped. This does not matter as long as the post is above the lower limit you previously noted you will get consistent shots but fewer of them per part fill. As an experiment I carried on topping up as many times as I could before there was no longer enough pressure to raise the indicator above its lower level. From the 15” barrel Spitfire I got almost 200 shots.
Due to over enthusiastic use of a flapwheel the main sealing surface inside the air reservoir of the first batch of rifles was damaged. This caused a slow leak. Did they scrap the faulty components? No. The answer that BSA management had to the problem was to go ahead and launch the Spitfire with these faulty cylinders and state that the rifle was designed to hold a “transient charge”. It would hold air for 2-3 days. This was stated in the instruction leaflets that came with the Spitfire. Who wants to buy a pcp that leaks from new. Certainly gunshops would not touch them with a bargepole. NOTHING CHANGES DOES IT!!!!!! This effectively killed sales. Marketing reported in addition that in a gunshop it looked too much like a springer to attract attention.