PURPOSE: To obtain a liquid bursting charge collectively injecting type bullet using a regenerative piston having a ramp function type booster charge output by forming grooves extended in the longitudinal direction on the external surfaces of the partial aftermost and partial forefront section of the bullet.

CONSTITUTION: A bullet body has two rotational bands 300 and 302 and a base section accepted by the neck section 306 of a case 30. A plurality of grooves extended in the longitudinal direction is formed on the base section and the front end of each groove is extended forward beyond the front edge of the neck section 306 adjacent to an annular projecting section 310. The grooves form a direct route for making a combustion gas which is generated from a booster with a relatively lower pressure to escape from the case 30 or prevent the abrupt shock of the gas with a high pressure which occurs when the bullet body is discharged from the case 30. The firing pin of a bolt gives a blow to a primer pouch 30a and the pouch 30a is ignited and ignites a booster 30b. The combustion gas from the booster 30a is firstly blown out through the grooves in the initial stage and, thereafter, unfasten the bullet from the case 30 and moves the bullet forward.