I posted a similar thread just a week or 2 ago after I hit my 1st vein. There were some comments that discussed the dangers of injecting into veins, but the risk is fairly minimal as Santa said as long as you are not pinning next to arteries. Aspirating can keep you from putting the oil into your vein but you will still bleed a little because the damage is already done in that respect.
After I freaked out my 1st time I mellowed out. Hell, people shoot heroin into their veins all the time.
These are facts.
You could shot 250mg test e straight into your vein and nothing would happen (google it, not a rare story)
You could also inject 250ml air straight into a vein and you'd get short of breath but nothing would happen.
The medical standard is NOT to aspirate anymore.
I'm sure most of us has left blood work or even donated blood or just various health checkups... How many times has the nurse fucked up and missed your vein or even punctured it ?
To hold a vein, you'd need to be super steady and hold it in an exact position all while ignoring veins dont "run" in a position where you would hit in in the right angle anyhow.