I recently aquired a broomhandle and did a some research on the net. This is a really good site I came up with:
C96 Broomhandle Info Site
According to this site, your pistol was produced between 1921 - 1930 (maybe your post of 1912 -1930 was a typo?). Anyway, it should have a Mauser banner on top of the barrel flat. The simplest guesstimation of the year your pistol was produced would be to assume a linear production rate between 1921 and 1930. Since your serial number falls directly in the middle of the given serial number range (500000-799999), the midpoint of the date range would be a general idea of when it was made (late 1925 - early 1926). Without more specific production data, this is about as close as you can come. I may be restating the obvious with this formula, but hanging around all these Luger guys makes you feel like an expert. In reality, I consider myself an advanced novice.
Here is a link to a thread with pics and info on my broomhandle (you have to register on this forum to use it):
Jack Lawman's C96 Broomhandle
Good Luck with your collecting,
Jack