Hi Paul,
I have owned and shot the full range of Feinwerkbau single shot CO2 match pistols and enjoyed owning every one of them.
The Model 2 was the first CO2 match pistol to be made by FWB and was the only one to have a loading lever - the others needed the loading hatch to be lifted to cock the pistol. It was also my favourite FWB CO2 pistol!
The steel CO2 cylinders were indeed given a 10 year life cycle at which point (unlike any PCP cylinder) they could be returned to FWB for inspection . When opened if there was no sign of corrosion the cylinder would be re-sealed and given another 10 year service life stamp!
If the cylinder was found to be corroded then it would be crushed and not returned. I am not sure if this service is still available but established UK FWB service engineers such as wonky donkey could probably be able to check the cylinder and re-seal it if it was seen to be corrosion free and safe to do so.
New replacement steel CO2 cylinders are still available although they no longer include the threaded end that allowed the optional disk shaped weights to be screwed onto the end of them (3 different weights available). I bought a new FWB steel CO2 cylinder from Buinger not so long ago and this came with a blank end-cap so I could no longer fit my cylinder weights to adjust the pistols balance. Fortunately the Model 2 balances really nicely and so this was not as much of a problem to me as it would be for anyone who preferred a "nose heavy" pistol.
The lower pressure of a CO2 pistol is often given as the reason why they are felt to be "kinder" to shoot than a PCP and this lower pressure (along with the use of steel) may also contribute to the possibility of non-corroded cylinders being able to have their service life extended.
I do not know of any commercially available conversion from CO2 to PCP for the FWB range of CO2 match pistols - and neither would I consider it an advantage either as it would destroy its "easy to shoot" feel - and that is why many of us really like shooting these superbly engineered match pistols.