As others have said, if they're black market they are almost for sure fentanyl... there are very few legit oxy 30s out there anymore, they stopped prescribing many of them and those with prescriptions use them for themselves. But there are MASSIVE quantities of fentanyl presses being sold as oxy 30s.
Even if they were legit oxy 30s, I would avoid this step. Oxy is MUCH more addictive than hydrocodone. Fentanyl is even moreso, plus it sucks, it's basically a hammer to the face. Plus they are notoriously badly dosed and one pill can give you a high, and the next can overdose you so bad that if you don't have a bunch of narcan, you will die.
Even if they are real oxys, you're treading down a much worse path than messing around with 10mg hydrocodones. Oxycodone is the real deal, and if you think you love hydro, you're gonna LOVE oxy... and that's a problem.
But yeah, again, there is very little chance they are actually oxycodone.