Hi. I had 1.
There were 2 versions of the AP40. First one's had an aluminium barrel. Later one's normal steel.
This also influences the pistol's balance. They were made from 2001 onwards I believe. Dunno when they discontinued them.
I found it a very nice pistol to shoot. Nice grip, decent sights..I actually preferred it over the Walther LP300XT 3D.
The cilinders had a downside; you filled 'em up to 200 bars, but at unscrewing from the bottle you always loose about 10 bars or so. Overfilling slightly is not an option, it'll blow its seals immediately.
Hammerli as such doesnt exist anymore though. Its now a part of umarex iirc, as is walther I believe.
Spares and service from Hammerli is AWFULL though, especially for older guns no longer produced.