i have a network between my computer and xbox, and
i can ftp into it.
someone told me that in order to hack the weapon projectiles
in halo 1, you had to change the cache with a hex editor,
but that doesn't work.

is there any other way of hacking the halo weapon projectiles ?

You can use the halo cache editor

You can use the cahce editor if you don't want to do anything amazing. Get HMT, and do it that way, it's easy and way more powerful that the cahce editor.