First Model Jennings was built in .54-caliber breech-loading single-shot configuration, with ring trigger, oval trigger guard and 26" barrel. A ramrod was fixed to underside of barrel as well. This variation was made from 1850 to 1851.

Second Model Jennings was produced by adopting improvements made by Horace Smith. Second Model is a breech-loading repeating rifle, with an under barrel magazine tube and 26" barrel. Frame is sculpted, unlike First Model. Ring trigger is still present, but trigger guard was removed as part of the design change. Caliber remained .54 and rifle fitted with 25" barrel. Second Model produced in 1851 and 1852.

Third Model represents an attempt by investors to use remaining parts and close out production. The .54-caliber Third Model was a muzzle-loading rifle, with a ramrod mounted under the 26.5" barrel. Same frame as used on First Model, but trigger was more of the conventional type. Trigger guard had a bow in the middle giving this model a distinctive appearance. This variation was produced in 1852 and marks the end of early conceptual period in repeating rifle development.