also it is possible you could get really sore on your first injection it's because you're injecting in "virgin muscle" just letting you know incase you get it that you don't get scared or something and wonder if you did something wrong. it's more likely this would happen in your quads the first time, happens to a lot of people (has happened to me as well), it doesn't have to do with the needle size it's because it's the first time the oil is being injected into your muscle. it's less likely for you to feel this in a glute injection but, I think some people still do, depends. I didn't feel soreness in my glute but, it is difficult to reach around etc. and I was shaking the first time I was doing it but, everything went fine.
These days I don't do glutes because of one time I drew blood and I started getting less careless as time went on and not paying attention I guess and hit it too high that's the reason I drew blood. I just rotate quads, delts (best spot for most people) and triceps (don't try this yet) and use slin pins for all shots. I still get soreness sometimes especially in quads so it's something that you will just have to get used to (but I just started these recently), I try to stick with delts because don't feel anything there but, it varies from person to person.