Are you asking us to tell you directly how much Oxymorphone it will take to kill you? That would be impossible to say even if we knew everything about you. I'm talking height, weight, BMI, condition of your heart, what is your current tolerance to this drug and/or Opioids in general. We'd need all of that in addition to all drugs and supplements you take.
I'm assuming by "bang" you mean that you're injecting your Oxymorphone? Keep in mind that there's a large difference between an addict's maximum daily dosage and the maximum daily dosage recommended by the medical community. The amount of Morphine an addict can consume as opposed to a pain patient is exponentially different.
What is your tolerance to Opioids? Preparing an oral formulation of Oxymorphone for injection, you are in essence, multiplying the potency of said dose by ten. Back in the day, when Oxymorphone was more widely used in the hospital setting, the common dose for Numorphan was 1mg - 1.5mg IV. So really, if you're not especially experienced with this practice, I would go slower.
Also, I'd be very interested in knowing how you safely prepare these extended release pills for injection. I don't want to hear your technique or anything, just to know that you actually have an effective way of administering without causing too much harm.