Oldarmy: See my comments on the other Pedersoli post by StaticX.
If you want a smooth finish, you will need to fill the open grained Walnut wood. I describe the process there.
Pedersoli Pistol Kit Post
As for pinning, the gun as it is designed will work OK. It really doesn't need a pin.
If you just want the experiance of pinning the barrel, there are two popular methods. The dovetailed underlug and the staple underlug. It is my understanding that both of them are PC.
Before you start off on this trek, be sure you want to invest the time to install the underlug, and take the risk of drilling the pin hole.
Risk? Yup. The crosspin hole must be done "blind" with the barrel installed. Because the barrel is installed, you can't see the underlug and if you mis-measure and drill the pin hole in the wrong place, or at the wrong angle, the pin will either miss the underlug, or hit the bottom of the barrel. :curse:
At least for me, drilling these pin holes on a gun is one of those semi-white knuckle experiances I never look forward to.
In fact, when it is successfully done, I've been known to take the rest of the day off.
Wet sanding is used when sanding metal or soft waterproof surfaces like paint, lacqure, dry True-Oil, Varnish etc.
The purpose of the water is to wash away the tiny bits of material which is removed. This keeps the material from plugging up the abrasive surface on the paper (I call it "fill").
Don't wet sand bare wood.
Most of the wet/dry papers are too fine of a grit to use on wood anyway. They "fill" rapidly and the cutting edges of the abrasive aren't really made (IMO) for working on wood.
The wet/dry paper works great on metal because it is made from silicone carbide (one of the harder materials man has made). ::