
In order to get the Firing pin out, you have to depress the end of the firing pin beyond the safety and then withdraw it to the left. (This assumes you took off the ambi safety on the right side.) Once the manual safety is out, you will have to depress the FP safety to let the FP come out the back. This is a painful operation and I do not do this often. I normally just shoot gun scrubber in followed by can air to dry it off. Then a drop of CLP for corrosion protection.
The frame is a little easier to deal with. The problem is getting all the levers to line up when you insert the hammer pin. Your first step to stripping the frame is to drive out mainspring retaining pin (#24). Once this is out, the grip will come off along with the main spring and plunger. The tension is now released off the hammer and the hammer pin (which is attached to the side plate assembly #57). Be prepared for a bunch of levers to drop. There are two little springs (#13) in the frame. Don't let those go missing on you. The sear pin and sear can also come out but there is no need to pull the sear spring. The disconnector (#6) will drop out either with the hammer or the sear.
To pull the drawbar (#7) you will need to drive out the trigger pin (#66).
To see where the trigger is making the gritty feel, look at how the drawbar makes contact with the hammer while in the single action mode. You can best see this after you pull the mainspring retaining pin out and drop the grip. Start with the hammer down in the DA mode. Observe where the drawbar makes contact with the hammer. This is where the drawbar grabs the hammer for the DA mode. Now cock the hammer to the SA mode and note where the drawbar makes contact with the hammer. It is forward of the DA contact point. The drawbar drags on this surface of the hammer before the forward part of the drawbar hits the sear to release the hammer. I suspect this is the source of the gritty feel you are noticing.