Cross bow bolts are shorter and stiffer than regular arrows, and their acceleration curve is much more intense upon being fired ; Thus their spinal characteristics are very different. Increasing the weight to 150 grains adds more weight front of center. This causes the bolt to bend slightly more at release. As with regular arrows, the action of the projectile in flight to regain its straight state causes a self centering reaction. This stabilization effect improves accuracy downrange; and has long been known as Bolt manufacturers offer heavier brass inserts for high accuracy shooters.The newest arrows on the market "Brag " about their increased FOC and the downrange accuracy it yields. In our testing we found that the optimal compromise between speed and accuracy was achieved at 150 grains. Any more weight and speed slowed too much; any less and the archer would lose the ability to hold 3 inch groups at 40 yards at 350+ FPS.Extended Range:Cross bow bolts, due to their lower overall mass, have tended to lose their punch past 30 yards as their momentum drops off. This has kept the cross bow, as a 20 -30 yard weapon for most archers. By adding the extra mass FOC, we increase the momentum generated upon release. Combining this with the Bolt Sonics "Cut on Impact" design yields tremendous "KNOCK DOWN" power at 40 + yards. So the weapon is now effective at that range. Price is per 3 pack.