I think few would argue that the 6004 is the best looking air pistol of all time...but I have had many moaning about poor cutting of cards and even some pellets not getting fully down the barrel when fired.
The gun feels nice in the hand and its side lever opening is far better than the hammer opening on the HW models. It snicks open in a seamless process when going for the over lever, without having to alter your grip on the handle.. The trigger can be set as good as any after some messing about but is not bad straight out of the box. Its at least twice the trigger of the Gamo Compact. I would say better than a Rekord unit on HW rifle if not quite as good as a Steyr match pistol...so its right up there once set up..However, its the power of the gun that lets it down. Chronying the gun I was working on, revealed 326 fps with Finale Match pellets. This is a slow gun stock ...even for an SSP
On first inspection i checked the breech seal. The Original FAS 604 used a White, Nylon seal which protruded a good distance out of the barrel groove but the new O ring seal sits more flush in its housing. Its a nice idea of Chiappa moving to an off the shelf O ring which is cheap and easy to replace but they retained the original groove dimensions that FAS used for the thicker Nylon seal. Big error IMO...its too deep for the O ring. It is proud of the groove and could fool you into believing this must seal but on closing the gun it does not as O ring grooves only seal on their top dead centre, unlike the broad face of the 604 seal. Its the angled face of the breech bulkhead which is causing the problem. When the seal comes down onto the bulkhead face, the top of the O ring is not quite sealing and the base of the steel barrel nicks the bulkhead face...putting a tiny groove into the face over time...I detected some blow by of gas at the top of the barrel where the O ring was barely contacting and estimated a good 30 to 40 fps vel loss.
To remedy this problem I machined a slim packing washer of stainless steel to fit in the base of the barrel groove. The washer thickness is 0.4mm. The O ring pushed on top of this gave a perfect seal with no gas loss detected and ensured that the barrel was clear from nicking the Bulkhead face. Chrony now showed 370 fps typical of this type of gun and cards looking much better, with clean holes.
This work can easily be carried out by using some Floss under the O ring seal, if you do not have access to a Lathe and you can stop here as i was now able to produce thumb nail size groups at 10 mtrs with zero mis fires.
I finally achieved 400 fps after more extensive work but the above work should help you with any breech sealing issues.
