Check if you bent the firing pin. Double feeds are notorious for doing this.The failures that I've been having is double feeds
Load mags as instructed above, keep them loaded when not in use and when bored, work the follower up and down with a stick or something. They need to be broken in.the round going in too angled up and it causes the slide to stop halfway. At first I thought perhaps it was the fact that the ammo wasn't hot enough like you mentioned, but the weird part is that if I only load 4 rounds it works really well. With 5 rounds it doesn't have so many issues but it doesn't run flawless either. But with 6 or more rounds there's a failure every 2 or 3 rounds. Another funny thing is that hollow points actually have worked really well, but at the shooting ranges here it's only jacketed rounds so I could only shoot 3 mags of HP, so I haven't tested it as extensively as the FMJ.