hi im a lvl 75 slayer and i often use a canon so i'll try and give u some advise best i can. the answer to the first question is very hard to give a specific answer for as it depends on the monster i normally take 1k canon balls on a task and depending on the monster / amount will some times return with 500 cballs left or very few. there stackable and so as long as ur fairly confidendt that u wont get killed easyily then having 1k balls on u makes sure u wont have to make extra trips just to get more c balls. the second question again depends if u get task like kalphites or dagganoths which are in multi combat areas u can go through between 1k-2k cballs and hours. your questions about how to obtain the cballs, you can continue to make them yourself if the smith xp is more important than the slayer speed. but if u start buying cball untill u get to higher lvls of slayer 75-80+ you will almost allways b at a loss in terms of money. the canon is mainly used to speed through task as opposed to lvling range and so wont really affect your range lvl that much it will enable u to level ur slayer skill at a much faster rate than without it. i hope i've been some help to u and havnt rambled on to much