Morphine has a horrible oral BA, in the 20 some % neighborhood. That means that if you eat 100mg oral morphine, you're only absorbing 20 some mg, the rest is just excreted with no effect on your perceived effects of the drug. It's hard to answer your question if we don't know your tolerance/experience with opioid drugs, age, weight, metabolism, personal body chemistry, and the host of factors that play into how a drug will effect you. Preparing MS Contin for injection is a pain in the ass IMO, and you don't want to miss the vein with pills. That's asking for abscesses which could progress to sepsis. I almost lost an arm in my early 30s (10 years or so ago) because of that and had to have surgery and a 6 day stay in the hospital on IV antibiotics or sepsis would have set in and cost me my life.
The instant release pills are easier to prepare for injection, but it's best to take your pills PO, as they are intended to be taken. If you are getting them by prescription you may be subject to piss tests and pill counts at any time. Depending on your DR, any perceived track marks and/or unaccounted for pills missing from your bottle could be the excuse they need to kick you off (usually without a taper), thanks to the fake "opioid crisis" the govt. and media have created. I am a chronic pain patient myself (20 + years and counting) and they are making it harder every day for those of us who actually, legitimately need them to get them, especially strong enough opioids in strong enough dosages to give sufficient relief, mobility, and some quality of life. It's a sad state of affairs that America has it's priorities ass backwards and have basically declared a war on chronic pain patients. Use/abuse of these ever increasingly hard to get prescribed opioids by people with no Earthly need for them, which many of us legitimately need to have some kind of quality of life, gives more ammo to main stream media and the govt.'s fake opioid crisis and the opioid hysteria which drives many of us to heroin, jail, or suicide. Just something for not just you, but anyone taking opioids they don't need, to consider and think about how much harder it makes it for us legitimate CPPs to get the medications we need and our lives that much harder; Not that anyone seems to give a shit, especially our govt.