Fmj for defense sounds risky. Tiny wound tracks and almost a guarantee to over penetrate even in 380. I would just continue using the HST before I used Fmj unless that's all I had. I will pick up a box of Arx and see how it goes. I figure if the flat nosed Wwb feeds, anything should. Have you tested those rounds any? I seen a YT vid of them testing though a windshield and it basically turned to dust. I don't plan on shooting windshields mind you. But I wonder how they fair if they hit bone, will they disintegrate into dust or keep going?
I have generally carried round-nose FMJ ammunition in my EDCs, asmy mindset is
somewhat of: if I'm having to draw and shoot for defense, anything is better than nothing. I know, I know...a plebeian mentality, I'm sure.
However, I did just pick up some Inceptor ARX ammunition for my Spectrum. I have not had a chance to get to the range with it yet, so I'm of no use to the OP with regard to performance. I will be following this thread with interest, though, and will post up if I get a chance to try it out.
I will note that Inceptor makes some decent frangible ammunition that worked well in my G2. (Frangible ammunition was a requisite for my indoor NRA Basic Pistol course a few years ago.) It fed/fired without error and was quite accurate for my needs at the time. I'm hopeful that the ARX .380 ammunition is of similar quality and result consistency.