I'm a Hammer's fan, having read most of the stories.
There really is no specific chronology that is mandatory for reading pleasure. I'd say to read Hammer's Slammers first, the first collection of short stories, because it includes a beginning and an end to the Slammers era. There's an origin story detailing how the Hammers came into existence, and there's a story detailing how Colonel Hammer became President Hammer. I think all of the Hammers stories takes place between those two points.
A main character in one story may show up as a minor character in another story, but, for the most part, you'll follow the adventures of different characters with no real clue as to where that story fits in an overall timeline. There are about three characters that show up consistently, but not in every story, including Col. Hammer. Most stories are about the regiments officers and sometimes about the enlisted men.
The Sharp End is notable because it is a novel, not a short story, and the reader can tell that the story takes place late in the timeline, if there was one.
If I were you, I'd read whatever Hammers book you could get your hands on and disregard the order.
Or...if you must, the Baen omnibuses are supposed to be in a chronological order as set by David Drake, himself. And, I think he included a new story in each volume.
EDIT Also note that there are a couple of books that take place in the same universe as the Hammers but has nothing to do with the Hammers: Cross the Stars and The Voyage. The first of which is based on The Odyessy, while Voyage is based on Jason and the Argonauts.