For me at least, when i had no opiate tolerance at all and was just fucking around....
10mg of oxy snorted all at once would get me quite high, about the same as 25mg after keeping a daily habit for a few months.
~33mg of morphine sulphate (1/3 of a 100mg pill) parachuted would get me pretty damn high, about the same as snorting a 10-15 line of OC. after doing this every night for 1-2 weeks, I started doing 50mg at a time instead which would fuck me right up, not to the point of getting sick but I would be wasted. one time my friend who had zero tolerance and weighs 30lbs more than me parachuted 50mg at once and puked, etc. So I'd say ~33mg is a perfect starting dose.
parachuting one 100mg codeine contin pill would have me pretty fucked up. a little less than the ~33mg of morphine would.
snorting between 4 and 8mg of dilaudid would have me nicely stoned, and still would at the peak of my tolerance. this is a weird one, because as my oxy tolerance shot up from getting high all day on 30mg to needing ~80-100, doing half a dilaudid 8 would still get me pretty high. I don't know how this works, but one time I gave a buddy with no tolerance a 4mg line and he barely felt it, whereas I was on 80mg/oxy a day and my 6mg line got me shit housed.
as for heroin, there is no way of knowing before you try it, I've gotten stuff where a tiny line got me lifted and stuff where a big line barely did anything. start small, work up.
I'm a pretty skinny dude, 6'1" and 140lbs. Hope this helps.
EDIT: I'd like to add that 10-12mg of hydrocodone is in no way equal to 10-15mg of oxycodone, yeah right. orally I'd say oxy is about twice as potent by weight.