That would probably be really simple. In fact, I'll try to make the script FOR you.
Also, when you start up Milkshape 3D, just place a joint, then zoom in on it. It should be the size of those grid squares.
Use this script. Copy the whole thing, paste it over everything in the CS file, and use the ctrl + h thing. Replace "YourWeaponName" with your weapon's model name. You won't need sounds, a bullet model, shell model or anything like that. All you need is this script, your model, the description, and namecheck file.
//YourWeaponName.cs
//////////
// item //
//////////
datablock ItemData(YourWeaponNameItem)
{
category = "Weapon"; // Mission editor category
className = "Weapon"; // For inventory system
// Basic Item Properties
shapeFile = "./YourWeaponName.dts";
rotate = false;
mass = 1;
density = 0.2;
elasticity = 0.2;
friction = 0.6;
emap = true;
//gui stuff
uiName = "YourWeaponName";
iconName = "./icon_YourWeaponName";
doColorShift = true;
colorShiftColor = "0.25 0.25 0.25 1.000";
// Dynamic properties defined by the scripts
image = YourWeaponNameImage;
canDrop = true;
};
////////////////
//weapon image//
////////////////
datablock ShapeBaseImageData(YourWeaponNameImage)
{
// Basic Item properties
shapeFile = "./YourWeaponName.dts";
emap = true;
// Specify mount point & offset for 3rd person, and eye offset
// for first person rendering.
mountPoint = 0;
offset = "0 0 0";
eyeOffset = 0; //"0.7 1.2 -0.5";
rotation = eulerToMatrix( "0 0 0" );
// When firing from a point offset from the eye, muzzle correction
// will adjust the muzzle vector to point to the eye LOS point.
// Since this weapon doesn't actually fire from the muzzle point,
// we need to turn this off.
correctMuzzleVector = true;
// Add the WeaponImage namespace as a parent, WeaponImage namespace
// provides some hooks into the inventory system.
className = "WeaponImage";
// Projectile && Ammo.
item = BowItem;
ammo = " ";
projectile = YourWeaponNameProjectile;
projectileType = Projectile;
//melee particles shoot from eye node for consistancy
melee = false;
//raise your arm up or not
armReady = false;
doColorShift = true;
colorShiftColor = YourWeaponNameItem.colorShiftColor;//"0.400 0.196 0 1.000";
//casing = " ";
// Images have a state system which controls how the animations
// are run, which sounds are played, script callbacks, etc. This
// state system is downloaded to the client so that clients can
// predict state changes and animate accordingly. The following
// system supports basic ready->fire->reload transitions as
// well as a no-ammo->dryfire idle state.
// Initial start up state
stateName[0] = "Activate";
stateTimeoutValue[0] = 0.15;
stateTransitionOnTimeout[0] = "NoAction";
stateSound[0] = weaponSwitchSound;
stateName[1] = "NoAction";
stateTransitionOnTriggerDown[1] = "NoAction";
stateAllowImageChange[1] = true;
stateSequence[1] = "Ready";
};