In general, this would be a cut off lever problem
if the cut off lever is worn, or just not doing it's job, then it would cause the gun to have problems firing semi-auto
the lancer/specna combo is a bold choice
not sure why it would have high speed gears - these could be spinning too fast for the cut off to activate? {{or could the sector be shimmed too high to grab the cut off to trip it?}}
You mentioned the gun has a microswitch trigger - does that mean it also has a mosfet system? ---> does this have any active brake / precocking settings you can add/change?
perhaps the nozzle is too big? - is the nozzle from the specna gb, the same as what was in the lancer's? (down to the decimal mm?, so if it was 22.4mm, is the other also 22.4?)
If you have the confidence/experience to crack open the gearbox, then do so, as you'll need to manually cycle the sector gear to make sure it's tripping the cut off
may be some trial and error needed, or perhaps a new cut off needed (if applicable)
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