yeah i thought 45 would be to easy, i guess you can use some program like Gmax or whatnot to take a look at the building, i dont use it myself so i cant guide you there.
the other way to do it hm how i usually do it, is to load a gun with those bombs and then hop into the test server and change material damages values on the fly until i find the right one. you might want to set a fast respawntime on that factory when/if you try this method
place a textfile in your servers root, name it bombtest.con or what ever you want, place a copy of all the new damage values in there (the new 888 material) then change one value in the new bombtest.con
example
MaterialManager.attGroup 888
MaterialManager.defGroup 46
MaterialManager.damageMod 100
write in server consol "include bombtest.con" to update the server then shoot at the factory with your modded bombgun and see what happens, if it dies in 1-2 shot then you found a material that is used, if not repeat with next material in the list.