The 342KA is considered a hammerless bolt action. I guess this is because the firing action is enclosed in the receiver. I can attest that the mossberg 342 was built from 1960-74 as a target rifle and there is no harm in puting on a scope providing it has the slots for the mounts.
I shoot a couple Mossy 151s and a 152 (which also has the fold down front ) and use scopes on them all.( bad eyes too). At the range they have proven to be as accurate as many of the proclaimed "target rifles" and some "built to shoot 50 yards rifles. I enjoy them more in the actual field duty. At over a 80% hit ratio, even out to 150 yards. Do not knock the old girls as they have proven themselves for over 80 years. The shorter barrels do tend to limit the distance but with practice, them and you come into sync and can be very pleasing.