Jemal
Adventurer
OOC-withing 30ft i have manyshot, which lets me fire +1 arrow for each 5 points of Base attack bonus up to 4 arrows with each attack at BaB 16 (I have a BaB of 27) with a cumulative -2 for each arrow (-8 for 4 arrows per shot) PHB pg 97. My BaB gives me 6 attacks, rapid shot gives me 7, and haste will give me 8 (though I haven't used it yet). 7X4=28 I threatened a crit with a natural 20, with a longbow which has a crit multiplier of X3 , but I accidentally rolled 31 arrows instead of 30 so just ignore the last roll. And since I don't think it critted only 24 arrows would count (if 1s are auto misses) meaning 24 points of con dmg (480hp lossat 40 HD) plus the weapon dmg (minimum 28X24=762) or immediate death in a geyser of blood .
OK, biggest problem - Yes, It does let you shoot up to 4 arrows as a single attack.. HOWEVER, Manyshot is a Standard action, it is not used as part of a full attack.
Second problem - You stop gaining extra attacks from BAB at epic, you only gain a max of 4 attacks for your BAB, +1 for Rapid shot, +1 for Haste.
That's 6 attacks as a full attack(3 at your highest attack bonus-2, 1 @ -7, 1 @ -12, 1 @ -17), or 4 arrows with 1 attack roll (Highest attack bonus -6) as a Standard Action.