My first question is whether the un-set trigger is exceptionally heavy.  I've never had this happen in a Stevens, but a set-trigger Winchester I have needed the full-cock notch in the hammer stoned. 

Premod70 may be on to something.  Could be the screw is loose. Have you recently put more pressure on the main spring? Have you recently tightened all the frame screws?  The next question I have is how does the tension feel on the rear trigger, when you set it.  If there’s not much tension then the spring is probably the issue.  I recently fix a Ballard double set that would not trip the trigger.  The Ballard works similar to the 44 1/2 and there was very little pressure on the rear trigger.  Took it apart and found the rear trigger worn down where the spring contacts it.  Just remember that the 44 1/2 set trigger spring needs balancing if modified.  If not done correctly you can cause other issues.  Like not catching the full cock notch.
Bob

Success with the 441/2 set triggers ! I took it apart again and checked for broken springs, stoned the sear nose carefully, made sure no springs were binding against anything. I noticed the rear trigger was just barley touching the Pope style finger lever when the front trigger was touched. To make a long story interesting, half a dozen strokes with a fine cut pillar file to the finger lever and it tripped the sear every time. I probably removed .003 to.004 of metal but that was all it took. I must be a slow learner. 
Thanks for all the helpful suggestions. 
Gunny