You think wrong, it would just have to move a few grams more.
while it wouldn't be an extreme effect, it would be there.
actually the main trouble wouldn't be with the weight at all, but the fact that a bow is designed to shoot 1 arrow at a time, at the nock on the bowstring, if an arrow is positioned anywhere else (as it would have to be to fit several on at the same time), then the additional arrows would recieve only a minimal force from the bow, and be almost totally inneffective (besides being wildly innacurate), though you are right in that the primary arrow which is located at the nock would only be slowed slightly, assuming the bow had a decent draw strength.