You make things admin only by checking the clients variables isAdmin/isSuperAdmin.
If you want to do this for a weapon id suggest you change the Item::OnFire function using a package.
For example (Makes the gun admin-only to use) :
package GunAdminOnly
{
function gunImage::OnFire(%this,%obj,%slot)
{
if(%obj.client.isAdmin||%obj.client.isSuperAdmin)
{
Parent::OnFire(%this,%obj,%slot);
}
else
{
messageclient(%obj.client,"","You are not an admin!");
}
}
};Activatepackage(GunAdminOnly);
However it will still play the firing animation for non-admins, it wont shoot any projectile.
Hope this solves your problem ;D