Not sure how much the redlegs were out in the field in the 1880's, but generally field "uniforms" were pretty loosey-goosey, and a matter of comfort and expediency. There are numerous photos of troops wearing civilian holster and belts, and several company commanders had their own holsters designed, fabricated and issued. Capt. Fechet, G Co., 8th Cav, designed one and Sgt. Wm. Miller fabricated such a holster which could be used with the Mills belts by means of a skirt that was held to the body of the holster by a narrow strap and buckle. It was open-top, butt-rear. Of course, this was a cavalry outfit. Not sure where artillery troops figured, but they might have been in charge of a mountain howitzer or somesuch.