ill take your word for it but i did a search and this was posted by a member awhile back...
A lot of people (experienced people) do quad injections wrong. You shoot into your quad at an angle towards your knee cap. This results in less tissue resistance. Thats also why a 1.5 inch pin is fine, cause of the slight angle.
You should be injecting into the upper part of the vastus lateralis muscle (lateral midthigh area). Jab the needle in so that its inserted one inch toward the anterior aspect of the thigh. There are no important nerves or vessels in close proximity.
Its for an infant, but the principal remains the same. You also have much more muscle that an infant (hopefully), so it goes deeper on the angle. I just recently starting shooting quads and they are great. If you are doing them properly ... they will be completely painless.