Between 1842-45 the War Department classified all of its flintlock arms to determine which were suitable for alteration to the newly adopted
percussion system. The actual alteration of those muskets selected began in 1848 using the Belgian or "cone in the barrel" method and continued until 1857.
However the adoption of the .58 cal minie ball in 1855 spelled the end of the smooth-bored musket in US service and negatively affected the cone-in-the barrel
alteration which could not withstand the combination of barrel weaking caused by rifling and increase in pressure caused the minnie ball. To solve this problem other stronger conversion methods were use.
These methods included the Drum & Nipple conversion, and two versions of a bolster conversion.