George, thanks for the very helpful figures. During the Gettysburg campaign, summarizing available sources, it appears that the commissary train (which may have been a subordinate part of the quartermaster train?), and the separate ambulance train, were organized at the brigade level, while the ordnance train was organized at the division level. The reserve ordnance (artillery?) train was at the corps level. So the regiment itself may have been directly responsible for six or so wagons. On the march, the latter wagons might be sandwiched between regiments, but more often it appears the regimental wagons traveled together as a group in a brigade or division train behind most of the infantry. But ammunition and ambulances retained their separate identities because they would accompany the infantry forward, while the remaining wagons would be held back. It appears ammunition wagons were painted black to distinguish them. I don't know if other colors were regularly used; one source cites a headquarters staff wagon as being painted red.