Re the Mainspring, I reduced by two turns.. and no misfires result.

As I mentioend, iof yiou reduce it too much the trigger drage forward too fast / to strongly due to the fairly powerful trigger spring.

With 148gn H&N HBWC, here are some chrono results with Unique powder...
Warning: These loads would be unsafe to fire with flat base bullet due to the reduced effective "case" volume.

3.7gns Unique averaged 850 fps
3.3gns Unique averaged 766fps (most accurate load)
3.1 gns Unique averaged 696 fps

I will do chrono tests with Blue dot next time I'm at the range andf post these when I have them.