I read the reviews of the AFX-DX37 before buying mine. Bought on line so didn't get to try any on first. I went with what the chart said for my head measurement. The reviews were all over the place but generally they said the fit was more round. My head is more narrow than round so I figured I'd be doing some fitting modifications. Sure enough, when I got it it was painfully tight front to back but ok side to side. I snapped out the lining and ground out enough foam for my forehead and it fits just perfect now. (grinding foam can be a pain with the grinding wheel of the dremel catching and bouncing around. I figure a sharpened spoon or something like that would be much easier. Just take a little at a time and fit on your head frequently while removing foam.)
If I hadn't done this modification, I would not have even tried the next larger size cause I believe it would be like what you've got now. Think about your head shape and decide if you want to return it for a smaller size and go to work on the foam. That is, if you have the time and inclination to do so. Sorry for the run-on reply. Hope it's of some help.
Sorry, I don't know about the shell sizes.
