Since you invited flameage, I'll speak my mind. And try and help you out too.
The short answer is simple. It's tolerance. Oxycontin is the most prescribed narcotic pain killer in the country and one of the most popular street drugs as well. Do you really think those 80s were sitting around for so long that they started breaking down? I know you said you just started but I can hear the addict way of thinking already. Or you could just be retarded. Nevertheless, I will try and educate you.
However you need to give a little more info. Did you sufflate both your original 20mg oxy dose and the subsequent doses? Or did I read that right your first dose was just 10mg? Because if you didn't notice 80mg oxys are large pills. Lots of filler. Much bigger than they need to be. So anyway, when you blow a big fat line of drugs, a fair portion of it never touches the mucal walls of your sinuses. Those drugs will eventually drip down your throat, down your esophagus and into your stomach where it will be absorbed much more slowly. Especially if you had a full stomach. Not to mention, since you seem like kind of a moron who does not use proper insufflation technique, you probably snorted the shit out of that oxy. When you snort too hard, the drugs do not hit the mucal walls of your sinuses, they do not drip down to your stomach, they do not pass go and collect 200 dollars. They fly down your windpipe and in to your lungs where they are NEVER absorbed. In fact, drugs in your lungs is a bad thing. I actually answered some guy's question yesterday who was convinced snorting heroin had given him pneumonia. Now I didn't think he had pneumonia, but ground up pills and such will irritate the lining of the lungs and create small cuts that become infected. This could cause pneumonia or a host of other miserable problems.
There is a reason they don't make medicine for people to insufflate. We all know it's a faster onset of action. The risks don't outweigh the benefits, clear and simple. My advice to you is to eat your oxy, like I do. Take your 80, crush it up good, wrap it in a small ply of toilet paper, and swallow with a swig of water. This is called parachuting. Or you could just chew it, like I do. I found no noticeable difference to parachuting and I like the taste. One side note here regarding oxycontin specifically. The color coating has nothing to do with the time release. NOTHING. The pill is created using a waxy matrix. That is to say the whole pill is time release. So you do need to signicantly crush it up before injesting. Although I have found that even a finely crushed oxycontin does not hit as hard as the same dose of percocet or oxy IR.
Most people here eat oxy vs blowing it, although I am sure it has little to do with the health benefits. You see, oxycodone has a higher bio-availability or BA you will hear people say. What that means is that it more of the drug is metabolized and reaches a higher peak plasma level in your blood stream. This means that while snorting a pill might hit you a little faster, eating it will actually get you HIGHER. And last longer. That's right, higher and longer, AND safer. It's almost like they were designed to be taken that way...interesting.
Ok so I'll go ahead and tell you how I like to get the most out of my pills. People will tell you lots of things potentiate opiates. Grapefruit juice (you would need to drink like half a gallon for a real effect), benadryl, all kinds of things. Some work for some people, but I know what works for me and it is very simple and I'm not giving myself an ulcer by drinking large amounts of highly acidic juice everyday. I take my oxy on an empty stomach whenever possible. This will make sure it hits you as quick as possible. I doubt anyone would argue with that. Then I go about my business for an hour or so. Then I eat a good meal. Within 5 minutes I am in nod city. Dropping the remote control, letting ciggarettes go out, etc. The big meal jump starts the digestive process and the pill has already been broken down so the drug is absorbed extremely rapidly into your bloodstream and hits like a fucking freight train. I believe I have found the ultimate opiate potentiator....the meatball sub.
So in conclusion, if you really need to snort your pills, use proper technique. Small lines, insufflated only with enough force to get the stuff into your sinus cavity and not fall back out. Then wait 15 minutes and do some more, alternating nostrils. But if your drug is oxy, do yourself a favor and eat that shit. I have taking it every day for years now and if snorting got you higher, I would snort it. Trust me.
By the way, your tolerance is not building any faster than normal. There is a reason oxycodone is so highly regulated, it is addictive as hell.
Have fun and be safe man. Peace.