Well, after countless hours of messing around with Willow Tree and what not I have found an easier way to make your own weapons in borderlands.
NOTE: This is to help those who already have willow tree and all that good jazz.

First start off with the basic layout of the weapon to help you out. Looks like this:
Item Grade
Manufacturer
Weapon Type
Body
Grip
Mag
Barrel
Sight
Stock
Action
Accessory
Material
Prefix
Title

Now, to start off change your weapon grade to Scorpio.
Code:
gd_itemgrades.Weapons.ItemGrade_Weapon_Scorpio
Now make it so it has no Manufacturer.
Code:
gd_itemgrades.Weapons.ItemGrade_Weapon_Scorpio
None
This allows you to use any Manufacturer specific parts.
You are also allowed to use any manufacture material, even ones not normally available for the weapon
Any grip from that weapon type can be used as well.

Now you can follow through with the process and add what you want to the weapon. When you finished make sure to end with:
Code:
0
0
0
61