I was reloading some .38 specials using 158 grain semi wadcutters from a well known manufacturer. When I had finished 100 rounds and was inspecting them, I noticed that three were shorter than the rest by about the rim thickness on the cartridge. I thought it was odd so I had a close look (today's photo). On the shorter one there was a circumferential ring while there was none at the right. I measured (calculated from the photo) the diameter of the bullet at that point to be 0.298 inches. The diameter of the other one (at the same height above the rim) I measured to be 0.280 inches. The height above the bearing surface above the cannelure is 0.197 inches on the left and 0.219 inches on the right. You will also notice that the short one appears to be seated deeper.

Here are my conclusions:
1) The bullet on the left was driven by the rim of the seating insert in the seating die. That is where the circumferential ring comes from and that is why it is seated deeper.

2) The bullet on the right was driven by the top of the cup in the insert of the seating die. This is how it should be.

3) It appears to me that the bullet on the left somehow got whacked on the nose during manufacturing which shortened and fattened it.

I sent this off to the manufacturer to see what they have to say. In reality it isn't that big a deal because I only use them for informal target shooting.