coke isn't really the best drug for a beginner to IV. i've IVed morphine, heroin, fentanyl many many times and have got the technique down pretty well. i've also tried IVing meth twice, and ritalin once(only once cuz i was dumb enough to believe some idiots who told me it was like IVing coke), and oxycontin a few times as well. i rarely ever miss. if i do, it's usually because: a.) i re-used a needle too many times, or b.) because i'm slamming coke.
it's really weird. i've tried IVing coke about 4-5 times, and only the last time did i succeed. usually i insert the needle, register, and then start pushing the plunger while loosening the tourniquet. i never have any problems with most drugs. but with coke, i'll see a noticeable bump forming around the injection site. i have no idea what causes this. this always happened with coke, and i never got a rush. but recently, i mixed some coke with oxycodone, and booted that. on my first try the same thing started happening as i slowly pushed down. i pulled out as soon as i noticed this was happening again. although i could feel a slight rush from the heroin and coke in that 1/4th of a shot, i didn't feel comfortable finishing the injection--so i quickly switched to my right arm. this time i pushed the 1/4" needle all the way in so that it would be more secure, rather than risk slightly raising or lowering the syringe while i injected it. as soon as i registered a full rose, i pushed the plunger down again, much faster than usual, and to my surprise, it didn't form a bump. i got a very nice rush from it and there was no swelling.
i didn't understand why it worked that time, so i loaded up another half shot of coke and tried it again in that arm. and once again i was successful. my guess is, even though i registered every time, if you push the plunger down slowly as i normally do, the coke reacts with the vein and starts constricting it(coke is used in nasal surgery to constrict veins and prevent bleeding) and that leads to the needle being expelled from the vein. also, on those 2 successful shots, i wiped the needle off before injecting to make sure it had no coke residue on the outside to react with the vein before i could finish the shot.
i'm not sure if i'm right about this phenomenon. but i do know that coke is much harder to inject than other drugs, and is probably more dangerous to boot than heroin. also i've noticed that the swelling that forms on a missed shot of coke is a hard lump, whereas when i've missed with h on the rare occassions, it's usually soft bubble kinda.