For very authentic reproduction Confederate kepis visit Richmond Depot in Chesterfield, VA just west of Richmond. Their website is www.kabar44.com. Confederate kepis varied greatly as Jim mentioned. Buckles were rare except early war. Actual function as a chin strap was rare (thus no need for the buckle). The strap being mostly just decorative and not of substantial thickness. Buttons went from civilian buttons to flat buttons to any letter or state insignia. My personal kepi most often worn is a red satinette (deep red) crown with a black band as shown in "Echoes of Glory" for Virginia Light Artillery. We chose block "A" buttons but flat buttons were easily the norm. The hat has a pigskin band inside and is lined with what we all recognize as homespun shirt fabric of a plaid pattern. The visor is natural finish leather but dyed black with a sewn band around the brim. Natural undyed stitching. Visors of canvas/pasteboard, tarred or painted were issued as well depending on the depot and availability of material. I do artillery and their gear varied widely as most were custom made and not Quartermaster issue if an NCO or Officer. A lot of artillery usually came "from money" and had the means to have more adorned and fancier uniforms. Kepi insignia was rare unless from a well known unit (i.e. Washington Artillery) as shiny brass literally made for a better target. Keep it simple and keep the brim/visor straight, not curved like a ball cap. In dress the kepi should ride forward on the forehead and high on the back of the head.
Third Co., Richmond Howitzers