It will work, but only hits good when he's 50%+ hp, use diamond (e) or drag bolts (e) instead, work way better, and plus, ruby take away some of your hp in the process, which you can't always afford to lose.
I have 4 fire capes, done about 10 for friends, read my first message lol
And if the bolts spec, it mostly won't be a 76 @ full hp, most likely will end up hitting 50 or so, just use diamond (e) or drag bolts (e)
use diamond (e) bolts its the best way (better than dragon (e) because of expense) i haven't done the jad myself but my friend did it on his pure ranger (99 range 70 def 99 hp 43 prayer) and he basically owned the jad..... but whatever u do its your choice......
Out all the capes I've done surprisingly i've only used ruby bolts a couple of times and the highest hit I've ever done was probably in the 50's. It is very unlikely you'll hit high and I'd recommend just using diamond bolts (e).