Here is a link to a video I quickly tossed together on how to make the revolver cylinder using booleans as a guide, I hope you find it helpful.

Cheers,
ctbram

https://www.screencast.com/t/ZWExZDU2ZGQt

Notes:

1. It is best to delete history and freeze transforms before doing your boolean

2. Avoid short edges or small near zero surface area faces.

3. If your boolean gives unexpected results or your objects disappear completely check for:

a. flipped normals (turn off two sided lighting is a fast way to check for this)
b. make sure geometry is completely intersecting through at least one full polygon
c. clean history, freeze xforms
d. be sure geometry is manifold (no edges connecting more then exactly 2 polygons, no bow-tie geometry ie edges that intersect but have no vertex at the intersection, and finally no flipped normals)

4. Think about the geometry that will be created after the boolean and avoid creating near parallel edges that are right next to each other or faces with near zero surface area or edges with near zero length or vertices that are co-resident.

5. Remember you can use history after your boolean. To get the cutting pieces visible again so you can adjust them go to the hypergraph and find the hidden shape nodes and make them visible again (shift-h).

6. Don't go crazy with booleans, but also do not fear to use them! They can help you to get a start on a complex form and you can always just use the resulting shape as a template and build on top of it if it proves to hard to clean up.

Experiment with booleans to learn their quirks. Try to keep the shapes of the objects as simple as possible, ie if you are planning to smooth you don't need gazilian-sided objects (this is something you should think about all the time. Use as little geometry as possible to get the shape desired.)

Just a general note - Always think about edge flow. Try to keep the geometry simple and flowing smoothly around the model. don't be afraid to add edge loops to even out the polygon distribution, shore up corners and help smoothing interpolation.

Note on HOLES...

Sometimes when booleaning an object you will get holes in a surface. Maya considers any edges contained within a polygon face that have no connection to an OUTER edge as a "hole". A common error that can be quite frustrating is to attempt to fix the problem by cutting an edge from the hole to an outer edge on the polygon. Maya will print a nasty message and refuse to allow you to do this. The best solution is to just delete the entire face (like the end caps of this cylinder example) and then use bridge or append to polygon to systematically rebuild the entire face.

And one last thing...

Remember symmetry is your friend! Don't be afraid to destroy what seems to be most of your model and just work on the smallest symmetric part and then rebuild.

I hope some will find this little tutorial is helpful and it makes folks a little less intimidated by booleans. They can be quite a time saver if used for good and not for evil! (smile)