Shop have said I can return it, plus given me the name and number of their GBBR guy to speak to. Purchased from FireSupport who are awesome and who I will use again (and again, and again!)
Seems from the Facebook TM GBBR group this is a feature, not a bug. IE they all do this and people just accept it 🙄 Apparently the regular (non-marksman) sear is pretty good so may try that. The fit and finish on it is amazing, shame the double-bevel on the face gives this weird issue!
HOME FIX: If you are happy taking the trigger box apart look for areas inside the shell where the trigger bar is rubbing due to torsion of off-set spring tension. Gently sand the corresponding area on the trigger bar to reduce the friction. Bonus points for sourcing 0.1mm steel shims for the hammer, trigger and sear posts to prevent torsion friction 👍
EASIER TUNE: Under the "tail" of the semi auto sear (rear left of trigger box as you hold the lower reciever) place small squares of gaffer tape under this, stuck to the trigger box, to reduce the sear engagement with the hammer. Don't add too much and check that you can't accidentally trip it by cocking the gun then slapping it around like it owes you money 😁
You should end up with some nice smooth take up to a clearly defined wall then a shorter, crisp break. Total cost £0.03p.