The Erma .380 was the first pistol I ever purchased, at the same moment as a Ruger MKII with 6 7/8 Tgt. bbl. So, one well thought out and wise purchase (as I still use that Ruger MKII today, and it's always been an excellent pistol) and one emotion-charged first-time-buyer "gee that's neat" not-so-wise purchase!
I owned that Erma for probably 20-25 years. I ran maybe 2 or 3 boxes of shells through it. I only ever tried FMJ, as I'd never considered it as a defensive pistol, for the following reasons: 1) the plastic grips had a huge thumb rest on the left panel which made for a nice grip, but made it virtually impossible for your right thumb to engage the mag release, 2) the sights were authentic to the original Lugers...minimal, 3) the magazine only held 5 rounds, 4) it was virtually impossible to load more than 1 round into the magazine without the included loading tool, 5) the safety was very stiff, the lever was small and difficult to manipulate, and it moved in the wrong direction, 6) if you opted to forgo the safety by carrying with an empty chamber, you were left trying to manipulate that toggle action (rather tricky under stress with sweaty hands), and now only had 5 rounds.
So, I never bothered to concern myself with whether or not it would feed HPs. FWIW, it never jammed or in any way malfunctioned on me. Despite the sights, it was quite accurate too. I remember firing it with my Father, we were shooting at milk jugs at about 10 yards, and it was too easy. So, we started aiming at the lids on the milk jugs, and we found we could consistently shoot the lids (from the side, about a 1/4" high target, at best) right off of the jugs. We were both impressed.
Still, I always had a soft spot in my heart for that little pistol. It pointed like an extension of my finger, and fit in my hand like a velvet glove. The fit and finish (at least on mine) was superb. It was kept nestled securely in its original box, with the original price tag ($169.00), all the original paperwork and hang tag, the mag loading tool, and a neat little "Erma" stick pin that came with it. It was absolutely pristine, ANIB.
Then, one day I decided I really had no need for the .380 cartridge any longer. I sold my Sig P230 (which I now sorta regret), my Grendel P-10 (it worked fine...but I don't really regret selling it), and then, my dear little Erma. I made some money on it, but now, looking back...I feel as if I let it go too cheaply, seeing as it was absolutely immaculate. The last .380 I needed to sell was my Colt GM. Before I managed to rid myself of it, I ended up finding a good deal on a PPK, then a PPK/S, then a HSC, another Grendel, a CZ83...etc, etc. Now I have more .380s than I ever had before...and I regret selling that Erma. I know I'll never find another one in the condition mine was in (at least, not for a price that I'd want to pay!)
Your loading problems with that magazine may be because you don't have the tool. It wasn't anything complicated, just a little "T" shaped tool that fit over the plastic button on the mag follower to pull it down and make the loading of rounds easier. It shouldn't be too difficult to fabricate something...just make sure you don't damage that magazine, they're not easy to find.
Tim