
There's the gun stock.

And there's the grate on the front.

The easiest way to remove it is to saw through the seam where the grate was glued on, and to the grab the pieces of grate that now are only glued on the back with pliers and just twist them off.

Sand down the insides,

Until a home depot bushing (same thing as a coupler only it has a smaller hole in the back and is wider) can fit in.

Lightly hammer it in, because it's a tight fit.

Seal it with some hot glue, and now you can pretty much attach any barrel you want to this gun.
No ranges yet, I'll try to get some tomorrow.