Yep. You are right on about the bolt. The knob on the end is larger than the earlier models. That changed when they went to the 340 series (340, 342, 347).
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There is fellow called Kelvinator on this website that seems to have a very similar 342. There also seem to be quite a few 342 owners on the site. Perhaps if photos of the rifle were posted there, someone might recognize it.
From the Cheap Seats:
Howdy RaS ... you may find considerable help at the site ;; Good folk !
https://www.gatewaytoairguns.org/GTA...p?action=forum