Hi,
It is hard to help you without photos of the lock and trigger. Did you build the lock? The Ferguson has a simple trigger but the lock has no fly detent so trigger adjustment for a light pull can be challenging. It is OK to have a little rattle in the trigger at half cock although I prefer my triggers to always be in contact with the sear. Another potential issue is the sear on the lock barely overlaps the trigger lever because the stock is so thick at the tail of the lock. Hopefully, your trigger is still able to engage the sear at full cock.
dave