PegLeg, a revolver chamber isn't truly cylindrical unless it's bored straight through. I think M1917 revolvers were because it was easy to make them quickly that way. But most revolver chambers have chamber mouths that taper down so it's only a cylinder shape up to there. That part of it's a truncated cone.
I based it partially on this, but what the hell:

Other types of cylinders
An elliptic cylinderAn elliptic cylinder is a quadric surface, with the following equation in Cartesian coordinates:
(x/a)squared + (y/b)squared = -1.
This equation is for an elliptic cylinder, a generalization of the ordinary, circular cylinder (a = b). Even more general is the generalized cylinder: the cross-section can be any curve.
The cylinder is a degenerate quadric because at least one of the coordinates (in this case z) does not appear in the equation.
An oblique cylinder has the top and bottom surfaces displaced from one another.
There are other more unusual types of cylinders.
These are the imaginary elliptic cylinders:
\left(\frac{x}{a}\right)^2 + \left(\frac{y}{b}\right)^2 = -1
the hyperbolic cylinder:
\left(\frac{x}{a}\right)^2 - \left(\frac{y}{b}\right)^2 = 1
and the parabolic cylinder:
x^2 + 2ay = 0. \,
http://en.wikipedia.org/wiki/Cylinder_(geometry)