As Cheyenne points out, the 42 is a robust gun and needs pretty much maximum loads to operate properly. From my experience, I would say the 380 ACP round as a whole is meant to be run near max. I've used Zip but not in the 380 but I have used a dozen other powders and they have all worked if max or near max charges were used.
I have a couple handfuls of 380s running from the S&W Shield on back to first year Savage and FN pistols and every last one of them runs most reliably when at max or within a tenth or so of max. I generally load a tenth of a grain under and have two pistols that have an occasional bobble. And they are at opposite ends of the spectrum with one being a modern Taurus TCP and the other a 1920s H&R.
I use a Hornady Lock-n-Load measure with the pistol insert for the 380. It has been accurate and reliable whether used in a single stage or a progressive machine. The progressive gets used with spherical/ball powders as they meter well with the occasional stick or flake powders being loaded on the single stage. These powders show a little more variation which is one reason I load a little off the max if just throwing powder from the measure. I have an old Pacific and a more recent Lyman beam scales which measure these light loads with no problem.
