Hawk Mk1 Ser. No. 21615
Complete with .177 and .22 barrels, present from daughter. Cosmetically very good except for broken rear site. But performance was dire. I stripped it down ... the end block refused to move under spring pressure so I gingerly 'persuaded' it to move, expecting a surge as it broke free. Nope .. it wasn't moving because the spring was too weak to push it out. Spring was no longer than the cyclinder with no preload, and clearly collapsed Piston washer (ptfe) looked good, as did breech seal.
At this point I had a Titan XS spring (No. 7) advertised as being for the Hawk Mk 1-3. From the start it was clear it was too long so I removed a few coils to give about 2" of preload. I could tell by trying to fit it that it was still too much so reduced it to 22.5cm long and 27 coils. Fitted with marked preload (about 1") but not too difficult. Firing was a marked improvement with performance about on spec, depending on pellet. But action was somewhat harsh and noisy. Cocking was OK but I could tell it was not perfect; spring had been a fair fit in the piston but I doubt if I could have fitted a piston liner.
Then came Jim Tyler's recent AGW (August) article in which he fitted a Meteor spring as he felt the spring he had fitted was too strong. I had a Meteor spring (Titan XS again, No. 6) so stripped rifle down and fitted it. It was, again, clearly too long so needed cutting to fit to give approx 1 " preload again. I took the opportunity to make a form of spring guide ... but putting the guide in the piston, not a floating one as Jim used but a true guide fitting in the base of the piston. The guide was about 5mm shorter than the piston interior space.The end block acted as a top hat. Rifle is now much sweeter to shoot, much quieter and performs better in .177, reaching 650fps with Wasps but .22 has not changed. Just goes to show that a strong mainspring does not always equal more muzzle energy.
While doing all this, I tested the piston for air tightness. It was good but out of curiosity I added some oil to the stock fixing holes, sealed the breech seal and pushed the piston in. Oil was expelled from one hole indicating a leak from the cylinder. I guess it was via the screwed in block but decided that I could ignore it as the stock bolt would provide a pretty good plug. I did ponder treating it as I would an HW35 but noticed that the bottom of the cylinder was profiled and that the PTFE piston seal was similarly profiled ... so I left it alone. I have come across such leaky breeches before ... the last time was a rifle where the hole for the stock bolt had penetrated the transfer port channel. But on the Hawk the transfer port channel is too far away to be 'in the line of fire' as it were.
I mentioned the broken rear sight .. the part that incorporates the sighting notch had broken, although the main body was still present, pivoting on its pin. Remedy was to make a steel plate that I screwed and glued onto the body part ... a bit fiddly to fasten but it works. Elevation / depression is via the original thumb wheel with a spring underneath that pushes the new plate up. I do not think it has all the movement of the original but it works. The other fiddly bit is the small star washer that secures the windage screw ... I have yet to find a replacement in the same style but the old one is performing well.
So ..... thanks Jim for the Hawk inspiration.

Cheers, Phil