First gen Hudson Thompson two trigger pulls required on semi

I bought an old Hudson Thompson as part of an unfinished Aliens Pulse Rifle project. After many hours of work and great advice from John at PFCGUK, I have managed to get it to fire quite consistently on full auto, although semi is troublesome. The first round will fire but when you pull the trigger again it clicks, the bolt moves forward about 10mm then stops, you have to release the trigger and pull it again to fire, the bolt travels forward at a slower speed and with less force which often causes poor ejection. Very occasionally a similar issue happens on full auto, you get a 3-5rnd burst then it stops with the bolt at the 10mm further forward position until the trigger is released and pulled again.
Has anyone come across this before or have any advice on sorting the issue.
Many thanks

Hi,

One thing to look at is the trip sear. It sounds as though it is catching the underside of the bolt as it moves forward.

Part #40

https://mp40modelguns.forumotion.net/t5239-hudson-m1a1-thompson