I just assembled a new Lower Parts Kit on a RRA stripped lower.

when testing, I cocked the hammer back, it hooks the disconnect and won't let go.

I have to push the bottom of the disconnect down it unhooks and sets, and is now ready to fire. Fires fine, safety works fine.

I fire, then cock hammer back and get same thing. The disconnect won't disconnect.

I have put several of these together with no problem.

Suggestions?

Make sure the spings are on and in correctly.
Make sure the disconnector moves with no binding in the groove in the trigger.
Where the lower kit come from?

I just watched JP Rifle trigger tuning video and it describes how to tune it.  They recommend using a bench belt sander like that made by Dremel with the support plate squared to the belt.  The edge of the disco hook is sanded square and perpendicular to the long axis line of the disco.  A very little shave at a time and refitted and reshaved until it works.  See if you can find a diagram or call JP Rifles and see if you can download instructions because I don't know if I'm explaining this right.  

I would not do this with a bench grinder or hand tools.

springs are in correctly, compared to my two other AR's.

took out trigger group put in other AR did the same thing.

disconnect moves freely,

I did notice that when the trigger is let go, front of trigger (on inside) goes UP to push disco out of way but doesn't go UP enough. I mean just a HAIR. Looks like the front of trigger under disco, infront of pin, on inside was shaved too thin, doesn't push up on disco enough.

RRA lower parts kit.