"31 Cal" on Bolster

This mark, usually on the left bolster of the trigger guard, only occurs on later, 1-Line New York addressed models. It was introduced in 1863, from about serial number 235000.

It was used to prevent confusion when obtaining or loading ammunition with the 36 calibre Pocket Navy, which was produced from 1861, and the 36 calibre Pocket Police model from 1862. After 1863, ALL Colt percussion models had their calibre stamped on them in this way.

The picture below, top left, is the most common version in terms of the location and size of the stamp. After #330000 (1872) a smaller die was used - shown in the second picture (top right).

On guns designed at the factory to be engraved, the stamp was often repositioned to the trigger guard itself - as shown in image 3 - bottom left. However, guns will also be found, like the one bottom right that still had the stamp in the "normal" position, even in some cases with the engraving over the top of the stamp.


1 - Standard position , early stamp
2 - Standard position, later, smaller stamp
3 - Different position on an engraved gun
4 - Engraved gun with stamp in standard position