GARDNER and GARDINER are both names associated with inventors inventors of the Civil War. Both buyers and sellers tend to get the names confused and misunderstand what is going on. The GARDNER is a distinctly Confederate bullet type once thought to be made with two parts so that the paper for the cartridge could be crimped between. The GARDNER sometimes had manufacturing defects and was prone to burst when it was fired. The result is frequently called a BLOW THROUGH bullet. However, it was never intended to explode.
The GARDINER, on the other hand, was produced by the Union in experimental quantities as a bursting shell fired from a musket. It was cast of an alloy more brittle than lead and held a copper chamber containing a bursting charge. The fuse was in a nozzle facing the base or skirt of the bullet. The intent was that, when fired, the main propelling charge would ignite the fuse train and cause the shell to explode in a second and a half.
Possibly ten thousand of these were captured by CSA forces at Chancellorsville. Some were used by both sides at Gettysburg. No really successful EXPLOSIVE bullet was designed by either side. EXPLOSIVE BULLETS were controversial for many years after the shooting stopped. A discussion may be found in "The Rifled Musket" by Fuller. Ordinary solid lead bullets distort and flatten so much that surgeons may have thought they had exploded. It may also be possible that BLOW THROUGH bullets were removed by surgeons.
Additional information and illustrations will be added when practical. See my guide for CIVIL WAR BULLETS for a couple of good bullet books.
The bullet below is the Gardner variety, an plain musket ball. The Gardiner is closed at the base with a center nozzle which actually contained powder which acted as a fuse which burned into an enclosed chamber with a bursting charge. The Gardiners were not pure lead but a more brittle alloy which ruptured when the charge exploded. They sometimes appear rather more blue colored than pure lead bullets.