You can make it wooden pistol super invention

To make the peg gun, you'll first need to remove the spring, and place the two wooden pieces back to back so the notches line up near the center.
Next. make a marking on the top piece about half an inch from the hole, and an angled marking on the bottom. (see the picture for reference)
Just for convenience I went ahead and filled in all the areas that need to be chiseled out with blue pen.So grab your utility knife and carefully carve out all the areas marked in blue.

The long channels made in the center of the pieces are going to act as our gun barrel so play with them until a wooden matchstick can slide in and out loosely when the two pieces are pressed together.
The angled marking, marks the place where you'll need to cut a small notch. This notch needs to angle back to hold the spring in place when you replace it.