It's mostly the lack of decent leverage that the front trigger used alone has against the sear that results in the felt heavy pull.

The front trigger itself does not have much trigger spring tension on it all by itself. You can see that by pulling the front trigger with the rifle Uncocked.
What you feel is the weight of the spring that the front trigger alone must overcome in it's pull.
..Not heavy at all.

It's the somewhat poor geometry of the low pinned front trigger pivoting and then pushing up against the sear/kicker that makes you experience the heavy trigger pull.

It is in place nicely for the double set let off. But not so great a position for a single trigger pull.
If the front trigger was pinned/pivoted higher in the mechanism to the level of the kicker/sear,,the trigger pull would be much lighter (simple leverage) than they are.

You can replace the coil spring that powers the sear with a lighter one, that just makes less spring tension to overcome when pulling the trigger with the rifle cocked

But risk the sear jumping out of engagement with the bolt sear surface if too light.
It's a balancing act that needs some careful attention.

Polishing sear engagement surfaces can be done but should only be attempted if you absolutely can keep them square to each other and flat.
Usually best left alone as they are not commonly a problem from the factory assembly and any advantage in lessening the single trigger pull will be very small if felt at all by the shooter.