Help with fastcast slowing down bullet

function module.IceMeteor(player, character, staff, abilityNum, mousePos)
	local iceStats = abilityStats.IceMeteor
	local caster =
	local rayParams =
	rayParams.FilterDescendantsInstances = {character}
	rayParams.FilterType = Enum.RaycastFilterType.Exclude
	local behavior = fastCast.newBehavior()
	behavior.RaycastParams = rayParams
	behavior.MaxDistance = iceStats.MaxRange
	behavior.Acceleration =
	behavior.CosmeticBulletTemplate = abilityItems.IceMeteor.Hitbox

	caster:Fire(character.HumanoidRootPart.Position, (mousePos - character.HumanoidRootPart.Position).Unit, iceStats.MaxRange, behavior)

	local bullet
	local first

	caster.LengthChanged:Connect(function(activeCast, lastPoint, rayDir, displacement, _, cosmeticBulletObject)
		if not first then
			first = true
			activeCast:AddVelocity(cosmeticBulletObject.CFrame.LookVector +,0, iceStats.ProjectileSpeed))
		cosmeticBulletObject.Parent = workspace
		local blength = cosmeticBulletObject.Size.Z/2
		local offset =,0,-(displacement-blength))
		cosmeticBulletObject.CFrame = CFrame.lookAt(lastPoint, lastPoint+rayDir):ToWorldSpace(offset)

		bullet = cosmeticBulletObject

	useAbility:FireClient(player, "IceMeteor")

Hello, i need some help with bullets. I am making a projectile for a game I am working on, and I want the bullet to be slower than what it currently is. Reading the documentary all I can find is properties such as Velocity and Acceleration, which are both Vector3 values, and when I try to slow the bullet down by adding a -z value, the velocity or acceleration is no longer relative and ends up going one direction. Im not sure what to dom, any help is appreciated thank you

Try to use the direction (rayDir) to slow the projectile down; maybe a hundredth of that value every raycast?