Whatever reason you have for using that size needle, it's probably not justified. The short answer is yes, you will hurt your veins. Forgive me for stating the obvious, but every time you inject into a vein you poke a hole in it. That hole needs to heal, and if you're using a bigger rig the hole will be bigger and and take more time to heal. Not to mention if you're doing it all the time, you're veins will go to shit pretty quick.