One thing I would worry about with a gas ram is that they are always pressurized and could fail when not in use. I wouldn't trust it long term unless it was rebuildable.
adrian, the gas ram in a hw90 is a theoben gas ram. At least they were last time i checked... RX, rx1 and rx2... all the same.
that is funny, an RX2 will set you back close to 1000$... so will a theoben. yes, theoben may be prettier, but the HW will out last them by far. Says my sirocco, eliminator and SLR... the Hw90 is more rugged. The big difference in price that i have noticed is because the theobens are no longer made... so the few that are around get pampered and generally tuned. Not Poo pooing the Theobens, but The HW gas rams are nothing to sneer at. And to be honest with you, even a tuned theo trigger (my SLR) could not compare with my RX .20 with the Reckord (also tuned). The fact that the newer RX2 had a theo trigger puzzled me til i was told that the resettability was the factor to choose one over the other... on a Reckord, you must re cock the gun to reset the safety. And the fact that both are powered by a Ram that can be left cocked for long periods of time made it more convenient to use the Theo trigger.
I agree that Theobens were probably the nicest rammers ever built, but their collectible high price and scarcity makes them hard to obtain and harder to recommend to a new shooter. I used to have a Beeman Crow Magnum IV (Theoben Eliminator) in. 25. It was an excellent shooter and the most beautiful gun I ever owned. But it was heavy, long, clumsy, and too pretty for squirrel hunting in the brush, so I sold it and eventually settled on a chopped R9 as my rifle of choice. I also had an RX2 (HW90) that shot well, but I'm just not into long, heavy guns like that, so I let it go. I get much more joy out of compact rifles.The .22 Fenman has been on my radar for a couple decades as possibly the most perfect small game air rifle ever produced (if hunting with a silencer is legal in your region) and I once shot an Evo set up for sub 12 FT that I quite liked. I hope to find a Fenman and/or Evo to add to my rotation someday, but I'd be surprised if they could buy more enjoyment than the well-sorted HW, BSA, and Webley carbines I've found over the years for fractions of what Theobens cost.