Shoulder injection percussiosns in depth?

[Wayacrucis]

I'm currently on my first cycle of 500mg test/week. I have a log here:
Starting Weight 200lbs - Dbol and Test E - First Cycle

I'm only injecting my shoulders, because I have no one to assist me with glute injections and I strongly prefer shoulders over quads. My first 3 injections I had no problem (Using 1" 23g) and I've been alternating right/left shoulders every 3.5 days. I was injecting my right shoulder today and when the needle was half way I felt an unusual amount of pain, so I decided to pull the needle out. I had some blood come out right after, nothing crazy, but much more than when I usually pull out. I pulled the needle out, used a new needle and injected slightly more to the front of the shoulder without a problem.

I just wanted to know did I hit a vein or something that caused this much discomfort? My shoulder is ridiculously sore and I have a reasonable amount of pain. No bumps, redness or swelling. I've scanned through the site, but I wanted to know about the main veins in the shoulders and all the necessary percussions I can take in order to avoid hitting them. I know there is a big vein that runs through the biceps and the shoulders, I'm not exacly sure where in the shoulder it is located, but I'd certainly want to avoid hitting or scrimming it. Any info on shoulder injectins is appreciated. Thanks.

[Bossman]

You may hit or nick a vein every now and then. When I go through a vein I have more pain and obviously more blood loss then normal. If the vein is near the surface, I may bruise and sometimes I develop a lump towards the surface. I've had two incidents of blood literally squirting after I pulled the pin out of my shoulder 3' and hit the mirror and splatter my bathroom vanity. Very little pain, but a weird feeling. Always have a alcohol pad to put pressure after pullling the pin on every injection.