Hi, 23g worked fine for me in chest. Just a little scary cus my heart starts poundin, movin my chest back and forth like a swinging bloody hammock, haha, oh the fun.
That is one thing I have never tried. Unless you are doing multiple ed injections there are plenty of easier injection sites. I hit my delts, calves, quads, bi's, tris, and glutes. I just don't really want to jam a needle in my chest.