As a matter of course the percussion caps were packaged within each package of 10 rounds of ammunition. In this way the Ordinance Department would be issuing the percussion caps as they issued ammunition. The ammunitions manufacture would have no idea which size of caps to package with the ammunition that they made, because they would not know to whom that ammunition would be issued to.
So it became the problem of the Ordinance Department to sort out the needs of each company in each regiment. Therefore the need to standardize was paramont to the armys needs. Therefore a conversion of a civilian weapon to Military useage was generally, but not always, to convert the weapon to using the musket "Top Hat" cap.
This conversion was most easily done to percussion shotguns because that only involved the changing of the nipples of the weapon to accept the musket caps to make them "Military". It all goes back to the old Ordinance Department addage and poem of "For want of a Nail ... the War was lost".
It is the "little things" like the ease of using a musket caps over that of a pistol cap that can add up to the difference of winning or losing a battle in the Napoleanic era of warfare. It is these "little things" that are so mundane to the average writter and historian that fill in the blanks between the lines of the stories of the "great Battles" and grand movements to me.
It is not the story of Great Battles and clashes of armys to me, but the problems of getting just one wagon load of ammuntion from the factorys in Little Rock to the army at say Praire Grove that is the real war to me. There would not have been a Confederate or Union army at any battle had they not been able to get that little percussion cap to the battlefield and to the right weapon. That is what is amazing to me. And sometimes they didn't get them there.