Not trying to make any scientific claims or say that these tests were performed in any sort of controlled setting. However, I do think the final displacement of each bullet tells a story and I am adjusting my carry ammo accordingly.
We went shooting last week and tried a variety of SD ammo in my Glock 33, Glock 19, Makaorv PM, P64 and Keltec P3AT. My teenaged son really enjoyed shooting the P3AT and Makarov. He was shooting our P3AT at some wet phone books with the SD ammo we have been carrying around. It fed and shot 100% but we were a little surprised when we pulled a few out of the backstop. We had two of the metro-ATL phone books leaning on a bucket of water. All rounds from the P3AT passed through the two phone books and hit the water bucket. Several were recovered in the bucket or backstop.
The shots below shows two of many recovered Magtech 380 +P SD rounds.
The next shot shows a 357sig Speer Gold Dot LE round fired into the same setup as the 380 above. We fired over 25 rounds of this ammo and all that I recovered had expanded.
Winchester White Box target ammo on right for comparison.