Abstract: The armature of railgun relies on the electromagnetic thrust generated by pulse current to drive a projectile. The appropriate feeding position of armature helps to reduce the startup delay of armature, and reduce the redundant length of rails. The influence of feeding position of armature on electromagnetic thrust at startup position is studied. Theoretical analysis and numerical simulations of hybrid finite element and boundary element method show that the electromagnetic thrust on the armature gradually approaches a saturation, with the increase in length of the rails in circuit by changing the feeding position of armature. For a square caliber railgun, the armature acquires 99% electromagnetic thrust at the four caliber position. However, with the increase in the distance between rails, the feeding position should be far more from the breech for the armature to get the most thrust. The influence of breech buss-bar on the feeding position of armature is also analyzed. Compared with the lateral layout, the longitudinal layout is more conducive to shorten the feeding length of armature. Key

Key words: ordnancescienceandtechnology, electromagneticrailgun, fourcaliberrule, inductancegradient, finiteelementmethod, boundaryelementmethod, load