OP, I'm sorry, but the only way that we can tell you what is in that pill is for you to have it sent to a laboratory and tested. We could throw some wild guesses at you, but being that we are trying to reduce harm, we don't want to spread any information that we're not fairly confident in. So it's for this reason that we do not typically field drug identification questions. Basically, you have a pill with a brand. This is a way better head start than if you were just identifying a random powder, but that is about as far as you can get in terms of clues.
It's not really important, but an A51 Oxycodone 30mg tablet is actually not controlled-release, so the entire 30mg dosage would theoretically hit you all at once. What we must do now, is go off of the assumption that your pill is probably counterfeit and probably contains some kind of Fentanyl analog. If we are going to assume or make educated guesses, this is the only remotely safe conclusion that we can come to. As we all know, the Oxycodone market is severely infected with fake pressed OC's, Perc 30's etc. so the only way you'll know for sure is by getting them from a pharmacist.