Do a solid model of the barrel guide shown below. All four of the small holes are tapped .250-20 UNC 2B. They are tapped the entire depth, despite what is shown in the photograph.
![barrel_guide](http://www.manufacturinget.org/wp-content/uploads/2014/08/barrel_guide-300x260.jpg)
Click the image to enlarge.
Here is the real barrel guide:
![Barrel Guide](http://www.manufacturinget.org/wp-content/uploads/2014/08/Barrel-Guide-300x180.jpg)
Here it is being used:
![Barrel Guide](http://www.manufacturinget.org/wp-content/uploads/2014/08/Barrel-Guide1-300x180.jpg)