A permeable barrel for accelerating a projectile is provided. The barrel includes a plurality of holes through which gas can be injected to generate a gas cushion for the projectile. The gas cushion prevents any contact between the projectile and the barrel walls. Also the gas cushion helps to keep the projectile centered in the barrel throughout its travel.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
 The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the U.S. Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Laboratory.