Okay, so I picked up a pound of Autocomp and had time to do an actual comparison between it and the factory powder. My Bersa Thunder with a 3.5" barrel was used for the test.
I pulled apart 5 Winchester cartridges and replaced the factory powder with 4.3 grains of Autocomp. These, along with 5 factory Winchester rounds were fired from a rest, across a chronograph. The Autocomp rounds averaged 991fps (18fsp ES) and grouped just under 1" at 10 yards. The factory rounds averaged 928fps (89fps ES) and grouped under 2" at 10 yards. Because there was a difference of 63fps between average velocities, my first thought was that the factory powder and Autocomp were in fact quite different. However, since I didn't verify the powder charge of each factory round, and there was a rather large variation between velocities, I decided to repeat the test again with an exact factory powder weight.
This time I pulled apart 8 factory rounds and weighed each powder charge. I was surprised to find such a wide variation from highest to lowest. The factory rounds varied from 4.1 grains up to 4.4 grains with an average of 4.2 grains. This was obviously why I saw a higher ES in the first test. After seeing this, I suppose some of us reloaders are overthinking our process. I usually shoot for charge weights to 1 tenth accuracy but maybe I'm being too anal.
I then reloaded 4 rounds of each, Autocomp and factory powder, to exactly 4.2 grains. Again, I fired these across the chrono at a target set out to 10 yards. The Autocomp rounds this time averaged 958fps. The factory rounds averaged 943fps. Both had an ES of under 20fps and both grouped at about 1".
Now, I won't say that the factory powder is actually Autocomp, but I will say that they're definitely close in performance. So close in fact that if the OP is wanting to duplicate the factory ammo then Autocomp would be a great choice.
Since making this comparison, I decided to test my favorite 380 reloads again, this time side by side with Autocomp. Up till now my most accurate 380 loads have been with HP38 and CFE-Pistol powders. I found that Autocomp matches both of those equally, no better, no worse. Where Autocomp exceeded those powders is in the +P ranges. Using AC, I can now get 1000fps with a 90gn XTP from my Pico while maintaining great accuracy.
These are the two targets from the test using 4.2 grains of factory powder and AC. Ignore the .22lr hole, that was a friend being a smart-a$$ with a BuckMark before I took the pic.
