How to add material detection to TurboFusion's gun script?

Basically, it detects what material you're firing at. So, if it's metal, diamond plate, or corroded metal, it changes the bullet hole texture to a dent. I'm having trouble with figuring this out. If someone can help me, thanks!! Also, if you shoot something that's a model, and it has a "Humanoid" in it, it makes a blood splat on that person or creature that was shot, and makes blood splats behind them. I'd like the wound texture to be different from the actual blood splat, as well.

Granite, slate, grass, brick, concrete, cobblestone, and pebbles, plastic, and smooth splastic share the same bullet hole texture. Ice and marble share the same texture. Sand has it's own texture. And metal, corroded metal, and diamond plate share the same same texture. Wood and wooden planks also share the same texture (which are splinters.) Also, if the part is invisible, no bullet holes show up.

--Bullet hole texture script (in the script named "Settings."

BulletHoles = true; --This is whether or not bullet holes will appear where you shot
    BulletHoleTexture = "http://www.roblox.com/asset/?id=190093197"; --This is the texture of the bullet hole
    BulletHoleSize = 1; --This is how big the bullet hole will be in studs
    BulletHoleVisibleTime = 12; --This is how long the bullet hole will be visible for
    BulletHoleDisappearTime = 1; --This is how long it will take for the bullet hole to disappear

--Part in the gun's main script that creates bullet holes on parts.

function CreateBulletHole(HitPos, HitObj)
    CreateShockwave(HitPos, 0.3, 0.2)
    local SurfaceCF = GetHitSurfaceCFrame(HitPos, HitObj)
    local SurfaceDir = CF(HitObj.CFrame.p, SurfaceCF.p)
    local SurfaceDist = SurfaceDir.lookVector * (HitObj.CFrame.p - SurfaceCF.p).magnitude / 2
    local SurfaceOffset = HitPos - SurfaceCF.p + SurfaceDist
    local SurfaceCFrame = SurfaceDir + SurfaceDist + SurfaceOffset
    local HitMark = Instance.new("Part")
    HitMark.BrickColor = BrickColor.new("Black")
    HitMark.Transparency = 1
    HitMark.Anchored = true
    HitMark.CanCollide = false
    HitMark.FormFactor = "Custom"
    HitMark.Size = VEC3(1, 1, 0.2)
    HitMark.TopSurface = 0
    HitMark.BottomSurface = 0
    local Mesh = Instance.new("BlockMesh")
    Mesh.Offset = VEC3(0, 0, -0.05)
    Mesh.Scale = VEC3(S.BulletHoleSize, S.BulletHoleSize, 0)
    Mesh.Parent = HitMark
    local Decal = Instance.new("Decal")
    Decal.Face = Enum.NormalId.Front
    Decal.Texture = S.BulletHoleTexture
    Decal.Parent = HitMark
    HitMark.Parent = Gun_Ignore
    HitMark.CFrame = SurfaceCFrame
    if (not HitObj.Anchored) then
        local Weld = Instance.new("Weld", HitMark)
        Weld.Part0 = HitObj
        Weld.Part1 = HitMark
        Weld.C0 = HitObj.CFrame:toObjectSpace(SurfaceCFrame)
        HitMark.Anchored = false
    end
    delay(S.BulletHoleVisibleTime, function()
        if S.BulletHoleDisappearTime > 0 then
            local X = 0
            while true do
                if X == 90 then break end
                if (not Selected) then break end
                local NewX = X + (1.5 / S.BulletHoleDisappearTime)
                X = (NewX > 90 and 90 or NewX)
                local Alpha = X / 90
                Decal.Transparency = NumLerp(0, 1, Alpha)
                RS:wait()
            end
            HitMark:Destroy()
        else
            HitMark:Destroy()
        end
    end)
end