I think you'll find this thread of interest then
https://www.airgunbbs.com/showthread...t=Hammerli+403
I bought a 403 a couple of years ago - at least I went to see a chap who was selling a 403 and a 401 and ended by buying both! Both are very accurate, but not the most powerful or the prettiest of rifles (although I take my hat off to the guy who stripped the thick varnish off his 401 to reveal some lovely wood underneath: https://www.airgunbbs.com/showthread...t=Hammerli+403 ).
This may also be useful: http://anotherairgunblog.blogspot.com/. This guy has a useful blog post on stripping the rifle but you can't link directly to it - search Hammerli on the blog search box and you should find among his past posts.
Beware of how the trigger unit attaches to the cylinder. My 401's was attached by 4 M3 bolts (some say 6 but mine had 4). Trouble is the cylinder wall isn't very thick so there's not much for them to grip and it's easy to strip the threads. Consequently I found only one of them still gripped, the others having wrecked the threads were just sitting there. A highly dangerous situation, as it could have gone off by itself when cocked. The solution was to (a) not use it until I (b) got someone to tap them out to M4. Then you'll find that they like to be tightened up just so - too tight and they don't like it at all. The spring washers play an important role.