In 1853 the breech bolster was widened to move the nipple over slightly, making the bolster project out about 1/8" to the side of the barrel instead of flush as on earlier models. The caliber remained .70 smoothbore. The 1857 model was produced with a rifled barrel and most of the 1853’s were sent back through the arsenals and rifled, which were then designated 1853T (Transformed). Also in 1857 the 42 1/2" infantry barrel was reduced to 40 1/2" and most of the 1853T’s were also shortened. All parts are the same as the 1842 model with the exception of the breech bolster.