I researched and wrote the article "The Short Rifles of the Lewis and Clark Expedition" for Muzzleloader magazine back in Mar/Apr 2000. There are many misconceptions about the "short rifle", the name used by the arsenal, the War Department, and Meriwether Lewis for the rifle we now know as the Model 1803. It was also called the "short rifle" and "iron ribbed rifle" in later ordnance correspondance.
The contract long rifles in stores were in unsatisfactory condition, with many problems as pointed out by Michael Carrick in his article on an apparent early "short rifle". Many of these contract long rifles had poorly made locks, rusted locks, lacked depth in the rifling, and many failed proper proofing.
The fact is, Lewis had new rifles, locks, and parts manufactured at Harpers Ferry. We know this by reviewing his letters, and ordnance correspondance from Secretary of War Henry Dearborn and master armorer Joseph Perkin. As for the notion they used slings, this is based on a listing for musket implements procured from the Schuykill Arsenal (Letters of the Lewis and Clark Expedition). No mention is made in the L&C journals of slinging rifles, and they aren't pictured in Patrick Gass's 1807 journal with slings. While Lewis was later drawn with a rifle with a sling and swivels, it's a long rifle or fowling piece, and certainly not a "short rifle".
Dearborn aptly describes the short rifle (Model 1803) in his May 25th, 1803 letter to Harpers Ferry master armorer Joseph Perkin.
As for the Model 1803 featured by Kirk Olsen in his American Rifleman article, it has a Type II patchbox and Type III barrel from the 1815 production run, so it's not a Corps of Discovery piece.
Being supplied by at least a dozen Pennsylvannia gunsmiths, the contract long rifles were run of the mill long rifles following the contractors personal patterns (or school of style, if you will). The only specifications were that they were to be a specific barrel length and caliber.
We know that it took two months for the arsenal at Harpers Ferry to manufacture Lewis's rifles, and that he mentions progress on his "arms".
Carl P. Russell presented journal documentation on the Expedition's "short rifles" in his 1957 book "Firearms, Traps, and Tools of the Mountain Men. The ordnance correspondance in James E. Hicks "Notes on U.S. Ordnance, Volume I" bears this out, as does the letters of Meriwether Lewis and Henry Dearborn, and later Tench Coxe. There is no documentary evidence that contract long rifles were ever modified to become Meriwether Lewis's "short rifles", which we know as the Model 1803. The "short rifle" is mentioned four times in the L&C journals by Lewis, Clark, and Sgt. John Ordway (and this is before two burst and the barrels cut short).
Jess Melot of The Rifle Shoppe documented two of the earliest known 1803 dated specimens, numbers 14 and 94. Michael Carrick and others have thoroughly documented nearly every part of a suspected early production rifle. He graciously sent me pictures and it's quite intriguing.
Finally, it should be noted that Lewis's short rifles differed only slightly from the Harpers Ferry production pattern, for in December 1803 Dearborn suggested several improvements to the design- a larger rear sight, a brass band to the forestock, and a wider bell entry pipe.
The differences in the types can be read here-
http://therifleshoppe.com/catalog_pages/us_arms/(500)_History_Facts_Description.htm