I have a Highwall with a single set trigger. When I set the trigger and fire, the hammer doesn't fall all the way and the rifle doesn't fire. It works when I don't set the trigger. What do I need to look at to adjust/fix it?

Has this ever worked properly?  There needs to be a fly in the hammer that blocks the 1/2 cock notch.  If the fly is there check to see if it is possibly sticking.

Jack

Wcf3840,

I’d focus on what Jrlouis suggested.  Most likely there is either no fly in the hammer or it’s stuck.  When you fire from the unset position there is a tumbler that lifts the sear out of the full cock notch.  The hammer falls so quickly that you can’t release the trigger fast enough to catch the half cock notch and stop the hammers fall.  In the set mode, the tumbler flies up and knocks the sear out of engagement, but just barely.  The sear slides down the rear of hammer toward a he half cock notch but the fly prevents it from engaging.  Good luck.  Hope this helps.

Best to use lighter fluid / Naphtha as both a cleaner and a lubricant as it won't attract unwanted fouling or other types of debris.