Well contins are filled with oxycodone, are you talking about just extracting this stuff or actually turning it into heroin?
Wrong. MS Contin is Morphine Sulfate. However, OxyContin is OxyCodone.
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(Osmium: "Acetic Anhydride vs. Glacial Acetic Acid (GAA)", Chemicals & Equipment)4-Dimethylaminopyridine as a catalyst in heroin synthesis (https://www.thevespiary.org/rhodium/Rhodium/pdf/heroin.synthesis.pdf)
(https://www.thevespiary.org/rhodium/Rhodium/pdf/heroin.synthesis.pdf) you'll see that their preferable starting material seems to be Morphine Base. If you on the other hand check out the publicationOpium and Heroin Cultivation in Southest Asia (https://www.thevespiary.org/rhodium/Rhodium/chemistry/heroinmfg.html)
(https://www.thevespiary.org/rhodium/Rhodium/chemistry/heroinmfg.html), which deals with ghetto heroin manufacture, you'll see that they use either the base or the HCl salt without any preference.