huey, i am a little removed from the exact dimentions between the different pieces of brass so i won't be able to tell you exactly the diameters but i will tell you all that I know about the calibers. I have shot and chambered guns for all the above. 9x23 was the first attempt to solve the high capacity problem of stacking 20 rounds in a magazine and then expecting them to feed reliably. The 9x23 is a tapered case that has a thick web area to better handle the old 175 power factor loads. The length of the case is the same as a 38 super but the rim of the case does not stick out beyond the web. CP elite was the supplier of the brass. Starline then entered the picture and manufactured 9 super comp and 38 super comp brass. 9 super comp brass is very similar to 9x23 in that it is a tapered case. .38 super comp has the same case head diameter as the 9 super comp brass but the case is a straight case. So what does all this mean to the shooter? Most chambers are in .38 super. Most chambers are big. Most guns will chamber and shoot all the brass. The .38 super comp brass is the simplest choice for the shooter that doesn't want to deal with the large rim on standard .38 super brass. The .38 super comp brass has a small rim due to the strait wall case but it works very well. Tune your extractor and you will be fine. tawn