I've not built any stripped lowers yet, but have a couple for projects.  On one lower I bought from amteec (preassembled) a trigger pin slipped out of one side, so it is now canted with the spring pressure.

I was going to start with the DIY assembly guide and reverse the directions until I got it disassembled enough to remove the spring tension on the trigger pin and reinstall it.  Am I going to need to install a different type of pin here?  The hole does not look elongated, but obviously, the pin did work out (say 800-1000 rounds).  Any quicker route or advice as I start the disassembly?  This is for my plinker, so I'm not fretting all that much.

Is this one of the things the KNS anti rotation pins fix?

I wouldn't sweat it the first time it happened; the hammer spring may not be installed correctly on the hammer providing insufficient tension or the legs of the hammer spring may not of been sitting properly in the slot in the hammer pin.

Reasssemble it properly and see if it repeats.

The KNS pins are really "anti walk".  It doesn't make a difference if a trigger or hammer pin rotates while being fired.  It is a problem, however, if they "walk" on you as you have described.  I have KNS pins on all my AR's and never give them a second thought.

MadDog