I see this all the time - the idea that in the .380 ACP you should be using ball ammo due to concerns about inadequate penetration.
Close on the heels of that I also usually see comments about concerns that heavy clothing will cause the hollow point to plug and fail to expand, and thus FMJ is a better choice.
And finally I see comments that bullets with polymer tips are a better choice as they won't plug and will expand.
Those three thoughts are not all that consistent with each other or all that logical.
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Here's my take on it based on my own testing in ballistic gel.
First, the Hornady 90 gr XTP (the XTP, not the polymer tipped FTX) is never a bad choice for a self defense bullet in a .380 ACP, provided it feeds reliably.
Provided you can get at least 975 or so fps muzzle velocity it will reliably expand in bare 10% ballistic gelatin and provide about 12-13" of penetration.
This was shot in a 2.75" Kimber Micro. Velocities for these two shots were right around 990 FPS.
On the left are three 90 gr XTPs fired from a Kimber Micro .380 ACP and on the right are three 115 gr XTPs fired from a Kimber Micro 9 9mm Luger.
If it fails to expand in heavy clothing so what? It will act like an FMJ. In other words FMJs will fail to expand 100% of the time, while the 90 gr XTP at 950 tp 1000 FPS will expand 100% of the time in bare gel and about 60% of the time in a 4 layer denim test with a few more inches of penetration. At 1000-1050 FPS performance in bare gel is the same and heavy denim expansion increases to near 100%.
Second, the more concerning failure with a .380 ACP hollow point is under penetration, where it expands just fine but on.y achieves 8-10" of penetration.
A lot of people suggest polymer tipped bullets like the Hornady 90 gr FTX. I don't have any photos handy with .380 test results but I do have some 9mm FTX results in a CZ75 Compact PCR.
Velocities were not excessively high at around 1050 FPS but performance was underwhelming.
In short, those polymer tipped bullets can give good penetration and expansion, but they are almost always suited to very short barrels where the lower velocities allows for slower expansion and better penetration.
Third, hollow points are preferable in a self defense round not as much for the expansion but rather for the limited penetration to keep it under 18". That maximum ballistic gel penetration figure is associated with ensuring the bullet doesn't exit the intended target and hit an innocent bystander. Hitting a bystander is bad for an officer in an officer involved shoot, but they have some degree of immunity as well as department funded lawyers and liability insurance backing them up.
As an armed citizen, you don't, so think twice about your priorities when deciding an FMJ round makes sense. Even in .380 ACP, I almost never see less than 22" of penetration in bare or 4 denim gel tests.
The only time I'd use an FMJ in a .380 ACP would be if the 90 gr XTP would not feed reliably.