Actually the regiment I am researching is the Union 1st Arkansas, which was organized during summer 1862. Their equipment returns show both the .54 and .58 caliber versions of the rifle which, of course, complicated things somewhat.

At one point in May 1863 Company K of the regiment was relieved of duty at Crane Creek, Missouri and rotated back to Springfield. Before leaving, they were ordered to turn over to three other companies enough .58 "Whitneys" to arm every man in those companies with such a rifle. If there were not enough .58 to go around, they were to turn over .54s to make up the difference. They were also to bring back any "odd guns of other descriptions--carbines, muskets, rifles, &c."