I tried a pec shot one day for the hell of it. No reason except to do it. I went about 2 inches above the nipple and then went straight in. The shot was painless.
I did have feeling like it was knotted and needed to be streched out. Which I did. Went away in about 1 hour. I would do them again if I needed to.
I'd sure as shit hate to get an abscess there more than anywhere else.... I'd just stick with human grade for those (and I mean real human grade, not some of that UG stuff that is made for humans therefore = human grade to some people, LOL).