Decompile system.mrs and open zitem.xml with notepad. Once you do that, look for the coding of the weapon type you want to make, for example, if you want to add a sword, copy the coding from a sword that is already made correctly and working, and edit it to your liking.
This is an example code part from one of the custom swords ive made, i put next to them what they are, if i didnt list what it is, its not really important and you should most likely leave it alone. Also, since this is a sword it doesnt have maxbullet and magazine, but magazine is how many bullets are in a clip, and maxbullet is how many bullets the gun holds total.
Code:
<ITEM id="999046"
name="Flame Sword" <-- Name that shows up in inventory
iscashitem="false"
mesh_name="flamesword" <-- This is the name that is in model.mrs
totalpoint="0"
type="melee" <-- Shows if its melee or ranged
res_sex="a" <-- Shows what sex can use it. (f= female, m = male, a = all)
res_level="99" <-- Shows what level it is to use it
slot="melee" <-- Shows what slot the item goes into
weapon="katana" <-- Shows the type of weapon it is
weight="5" <-- Shows the weight it is
bt_price="0" <-- Shows how much it costs if you add it to shop
delay="300" <-- Shows the delay
damage="9999" <-- Shows the damage
range="200" <-- Shows the range the weapon has. (Normally only on melee weapons)
ctrl_ability="0"
magazine="0"
reloadtime="0"
slug_output="false"
gadget_id="0"
hp="0" <-- Shows the HP bonus of the item
ap="0" <-- Shows the AP bonus of the item
maxwt="0" <-- Shows the Weight bonus of the item
sf="0"
fr="0" <!------
cr="0"
pr="0" Shows elemental resistance bonus of item
lr="0" ------!>
color="#FFFFFFFF"
image_id="0"
bullet_image_id="0"
magazine_image_id="0"
desc="Bored with nothing to do. Modeled by Mike." /> <--- Shows the description that the item has
Hope i helped ^.^