PS-F2V2-M4 Polarstar F2 V2 Conversion Kit, M4 / M16 Cylinder (RED / SILVER)FEATURES: STABILIZES THE BB IN THE HOP UP BEFORE FIRING FEATURES A LIVE FIRE TUNING SYSTEM REMOVES ANY SPIN THAT MAY CAUSE BBS TO VEER IN A DIFFERENT DIRECTIONS AT RANGE. IMMEDIATE TRIGGER RESPONSE WITH NO FIRST ROUND SHOT FCU TO ADJUST KEY SETTINGS AND MEET FIELD REQUIRNMENTS 2 9RD BURST CAPABILITIES F1 MADE COMPACT AND EFFICENT IMPROVES HOP UP PERFORMANCE WITH A WIDE RANGE OF STOCK AND AFTERMARKET OPTIONS COMPATABILITY BETWEEN F1 AND JACK SYSTEM