Above is a view of the Maynard priming device on a replica M1855 rifle musket (click on the image to open the door).  As the primers are no longer manufactured the cap-magazine is a non-operational dummy.  With the door open, however, you can see the cavity, deeper in the originals, into which a soldier would place a roll of 50 caps before firing the weapon.

     Also absent in this copy but present in the original magazine was a small steel hand for advancing a cap over the cone every time the hammer was cocked.  The weapon was loaded with ball and powder from the muzzle, and, after driving the round home with the ramrod stored in a groove underneath the barrel, the rifle was cocked, advancing the primer, and fired.  The explosion of the cap when the hammer fell on it caused a spark to travel down the hollow cone and set off the charge of gunpowder.  On the lower part of the hammer also had a cutting edge to cut off detonated caps

      This roll cap priming system was called the "Maynard primer" after Dr. Maynard, a dentist who wanted to be a soldier and spent much of his free time designing weapons.  Besides the roll caps which he invented in the early 1840's Dr. Maynard is also recognized as the inventor of one of the first efficient breech loading cavalry carbines.

      The M1855 family of weapons could also use the 'common musket cap,' a tiny inverted copper cup that contained an explosive charge.  The common cap fit snugly over the cone and when fired it performed the same was as the Maynard cap, the only difference being that the spent cap had to be removed by hand and a new one put on the cone before the weapon was fired again.  The common cap was first used in U.S. service with the 1841 'Mississippi' rifle.

      By 1861 it was decided to omit the Maynard primer in favor of the common cap in future U.S. arms as the Maynard primer had a tendency to mis-feed and exposure to any moisture rendered the rolls of caps useless.  The Model 1861 Rifle Muskets retained, however, the distinctive arched hammer that was originally designed to close over the door of the Maynard primer magazine of the M1855.   In Confederate service the Maynard primer was also abandoned, although early war 'C.S. Richmond' rifle muskets, made on the machinery taken from Harpers Ferry, had a blank plate under the arched hammer exactly where the Maynard magazine was located in the M1855.