Gravitic lances were recent weapon developments during Miles Vorkosigan's lifetime. They required bulky power packs massing several hundred kilos, thus they were not used as hand weapons.
A ship armed with a gravitic lance had to make an extremely close approach to its target; when two ships attack each other with lances, the battle was typically compared to playing a game of chicken. Effective defenses against gravitic lances did not exist during the time of the Vorkosigan Saga.
The physics behind gravitic lances was described as a "five-space/three-space interface phenomenon."