3 shapes of powder chambers

[Cat Whisperer]

Here is one (old) reference to 3 different powder chambers (and a lot of other topics).  Makes interesting reading.

http://www.usregulars.com/gibbons/gibbons_chapter_ii.htm

Note the three kinds of chambersin Figure 13: the cylindrical (A), conical (B), and spherical (C).

There are other good discussions and other perspectives, but this gives a 'period' explanation of the times.