Once needle is in muscle, how hard to I have to pull back on plunger to make sure that I haven't hit a blood vessel?

Like today I was injecting 1 mL of Test E 250 and I was pulling back on the plunger and the plunger wouldn't move but I wanted to make sure that I wasn't hitting a blood vessel so I put some effort in and a few bubbles shot back into the syringe.

I asked my buddy this question and he said that very little effort has to be done and you just pull back lightly and if there is any blood it will shoot right up into the syringe.

Any help would be greatly appreciated. Thanks guys!