This thread is a Glock 42 vs Glock 43 Ballistic test (not a general caliber test). I chose to put it in General Glocking so people can see the difference between a G42 and G43 in gel tested back to back with different popular ammunition and make their best educated decisions on what trade offs they are willing to make. Some of my previous testing: My first test: Getting a sense for 380 vs 9mm in different barrel lengths https://www.glocktalk.com/threads/quick-ballistics-test-g42-vs-g26-vs-g34.1654105/ Testing different 380 rounds https://www.glocktalk.com/threads/quick-g42-and-g26-ballistic-testing-hot-ammo.1658862/ Compilation thread. There are some fruit shooting videos here too. https://www.glocktalk.com/threads/quick-compilation-of-g42-ammo-testing-including-new-p.1659345/ Denim testing https://www.glocktalk.com/threads/quick-compilation-of-g42-ammo-testing-including-new-p.1659345/#post-24144777 Ham shooting for simulated chest https://www.glocktalk.com/threads/final-g42-ballistic-testing-xtp-over-xd.1661502/ 8 layer denim failure test https://www.glocktalk.com/threads/g42-hollow-point-failure-test-8-layers-denim.1662442/ After I had done those tests, I picked up a G43 and some Federal +P 147gr HST as well as a Makarov conversion barrel. See this thread for information on the conversion: https://www.glocktalk.com/threads/the-glock-42-with-the-9x18-lonewolf-barrel.1663739/#post-24251900 The questions I set out to answer (for myself): My gold standard G42 (380) ammunition is the Underwood 90gr +P XTP. It does a consistent 12.5" in bare gel with decent expansion. Would the G42 with a 9x18mm Makarov conversion perform better with commercially available ammunition (Hornady Critical Defense and Underwood +P XTP)? How would this compare to a G43 with different self defense ammunition (Federal HST +P 147gr, Speer Gold Dot +P 124gr and Speer Gold Dot normal pressure 147gr). The 9x18 Makarov cartridges: Underwood XTP +P (left) and the Hornady Critical Defense (right). And the difference in the XTP bullets in 9x18 (left) vs 9x17 (right). The 9x18 XTP is a lot different of a bullet than the 9x17 XTP. I was very curious to see how they would perform and whether there was a favorable ballistic difference. Everyone is a little different in how much penetration they are willing to accept. Personally, for a weak cartridge like 380, I am aiming for 12" of penetration knowing that if I penetrate much farther than that it's at the expense of energy delivery to target and expansion. I personally don't feel comfortable with 380 cartridges that expand a lot but penetrate a little. Like the Gold Dot in 380 which in my testing only penetrates ~8". So when I shot the rounds in gel, here were the results. I put markers where the bullet tract ended (there is a little gel bounce back, so the physical bullets may be behind the marker). This is a 16" FBI block of ballistic gel with another gel block past it. Here are the expanded bullets and the distances they traveled in bare gel. Side view of the bullets to get a sense for the dimensions of the expanded bullets. Discussion. I see it again and again. There's a very small sweet spot of penetration and expansion for each bullet and cartridge. I'm looking for 12-16" in bare gel. More distance almost always comes at a trade off of smaller expansion and wound cavity given the same caliber type. Also, for a given bullet: more velocity = more expansion and less penetration. I've seen this in different barrel lengths and in different higher pressure loadings of the same bullet. Conclusions: G42: The Makarov XTP bullet was too large of an expander, rivaling the results that the +P 380 Gold Dot did out of the G42. Large expansion, but not enough power for adequate penetration (~8"). G42: The Makarov Critical Defense penetrated "okay" but didn't give additional expansion over the tried and true Underwood 380 XTP +P. It also had some challenges with the factory extractor due to the large lip on the casing. G42: The 380 Underwood XTP +P in the G42 continued to perform consistently and will continue to be my SD ammunition of choice in that pistol. G43: The 9mm Federal HST +P 147gr was an excellent expander and penetrator. G43: The 9mm Speer Gold Dot +P 124gr expanded and penetrated well. G43: The 9mm Speer Gold Dot 147gr out of the 3.4" short barrel was too slow to expand well and consequently penetrated a little deeply. This was even worse in previous testing with a 3" Kahr PM9 where it went >19" and expanded even less. Disclaimer: Testing is for entertainment and education. If people can get something out of it, then great. I understand that testing self defense ammunition is overkill and theoretical as most people will never need to shoot a single round in self defense. I also understand that some people feel most comfortable with SAAMI spec ammunition and some are comfortable with hotter ammunition. I also understand that a 9x17 and 9x18 will not and never be a 9x19 and that some people view 9x19 as the minimum effective caliber / ammunition for self defense.