Log the "_ammo" array in the HitPart eventhandler on an infantry unit and observe the hit value and ammo class name being identical for both buckshot and flechette shells (6 and B_12Gauge_Pellets_Submunition_Deploy, respectively).
This can be verified in the ammo config, where both ammo types use submunitionAmmo = "B_12Gauge_Pellets_Submunition_Deploy";