Help with a material-based bullet hole system with ACS 1.7?

Hello, I am currently working on a custom version of ACS 1.7 and I wish to make a material-based bullethole system, I already have the basics of it so, when you shoot, it creates a bullethole on whatever part the bullet hit. Now, what I need is for it to be material-based, so basically, different bulletholes depending on the material of the part that the bullet hit.

The lines for this system to work are:

local default_bulletholes = {
    "4117124202";
    "4117124881";
    "4117125609";
    "4117126706";
    "4117127411";
}

and

    Evt.Hit:FireAllClients(Player, Position, HitPart, Normal, Material, Settings)
            local a = Instance.new("Part", BulletModel)
        a.FormFactor = "Custom"
        a.TopSurface = 0
        a.BottomSurface = 0
        a.Transparency = 1
        a.CanCollide = false
        a.Size = Vector3.new(0.5, 0, 0.5)
        a.CFrame =  CFrame.new(Position,Position-Normal) * CFrame.Angles(90*math.pi/180,math.random(0,360)*math.pi/180,0)
        a.BrickColor = BrickColor.new("Really black")
        a.Material = Enum.Material.Air

        local b = Instance.new('WeldConstraint')
        b.Parent = a
        b.Part0 = a
        b.Part1 = HitPart

        local c = Instance.new("Decal", a)
        c.Texture = "rbxassetid://"..default_bulletholes[math.random(1,5)]
        c.Face = "Top"
--      c.Transparency = 0

        local d = Instance.new("PointLight", a)
        d.Color = Color3.new(0, 0, 0)
        d.Range = 0
        d.Shadows = true

        local e = Instance.new("Weld")
        e.Part0 = a
        e.Part1 = HitPart   

Some help would be extremely appreciated.

My discord: krypto#0514