Please forgive my terminology in places, I'm no gunsmith so I've described bits as I've seen them rather than by their technically accurate names.
The trigger was really hard to pull on my Mod 70, and as a result I found my shots were all over the target at 12m (40mm groups!). The local Hatsan distributor has been advertising "new improved trigger", but I felt it was still excessively tight and couldn't be adjusted with the screw that goes through the trigger.
Apart from the sear that catches on the piston, there is a pivoted piece that holds the sear up, as well as a pivoted lever between the trigger and the piece that holds the sear up. I wish I'd taken pics but I hope my descriptions are of some help.
I had to cut away a bit of the plastic trigger where the adjustment screw goes, because the screw wasn't long enough to reach inside the mechanism to make any difference. I suppose a longer screw would have worked, but then at 9pm we don't have too many shops open where I might buy ones, so I "made a plan" and cut away a little bit of the trigger plastic (about 3mm) to allow the screw to penetrate deeper into the mechanism where it can touch on the pivoted lever that pushes on the piece that holds the sear up.
I also polished up all of the contact surfaces on the metal parts that catch and rub on each other as you pull the trigger, by first using sandpaper and then "Brasso", it left a highly polished surface (at least on the raised bits that were touching). I guess car polish would work just as well.
I cleaned off all of the factory oil and put in some Vaseline petroleum jelly between the moving parts and reassembled.
I had to straighten out the cage that houses the mechanism parts because the sides were flared open and there was excessive side play on the parts.
I also replaced the long spring behind the trigger with a "click pen" spring.
There is a sight hole in the side of the mechanism housing where you can view the contact between the sear and the pivot plate it catches on, and I adjusted the screw through the trigger such that the overlap between the 2 metal surfaces is about 2mm.
I then tested it and boy, what a difference! Where at 12m I had previously been spraying pellets all over the target in 30 to 40mm groups (I'm not a very good shot!) I was now shooting sub-15mm groups. The trigger is very light, I haven't measured the pull with any device, but I barely have to touch the trigger and it fires, I even backed out the screw a few turns just to be safe, although with my first screw setting I loaded the gun and banged the butt on the floor a few times and it didn't fire "accidentally".
I wasn't at all impressed with the pieces of metal they used for making up the trigger mechanism parts, they are stamped out of about 1mm steel plate, and then they use 3 layers riveted together to make one piece 3mm thick. The steps between the layers where they don't quite line up are left as is, as are the rough surfaces on the edges where the metal sheared while being stamped out of plate.
One further mod I'd like to implement would be to polish up the end of the screw where it rubs on the lever that pushes on the other pivoted plate that holds the sear up (if that makes any sense). When I have a little more time I'll make a drawing from memory of the parts, I'm not up to stripping the gun again tonight for pics!
Altogether, with the trigger the way it is now I'm very happy with the gun and scope, much happier than I was with my previous gun, a Gamo CF30.
The 4x32 Nikko Stirling scope it came with works very well, the scope mounts grip both the rails and the scope well enough that it doesn't move.
Does anyone have any tips for removing the plastic front sight? It appears to be moulded to the barrel.