What kind of 380 or 9mmK pistol is this? I normally use 90 grain cast bullets in my .380s, which mine range from a Grendel to a Walther, with some others in between. I used to own a MAC11, but the cases were bulged after firing them, but it was a Rock and Roller, so I figured I would loose a lot of brass.
I look at the 380 as the hidden last line of defense pistol, not as good as a 38 Spl +P but will do the job at close range like 5 feet.
Here are two Lyman loads from the 49th Edition of their Handbook
90 grain HC bullet Bullseye powder start load 2.0 grains MAX load 2.9 grains
115 grain HP bullet, Bullseye Powder Start load 2.0 grains MAX load 2.9 grains
Herer are the loads for Cast Bullets
90 grain RN bullets, Bullseye powder Start load 2.4 grains MAX load 3.0 grains
120 Garin RN bullet, Bullseye Powder Start Load 1.6 grains MAX load 2.1 grains
Mostly I prefer WW 231 powder for my 380 loads with a 90 grain cast RN
Start load is 2.1 grains MAX load is 3.2 grains I use 2.6 grains of powder for my reloads.
I don't have any data of 800X powder that I trust. What have been able to find says that the load should be 4.1 grains for the 90 grain bullet and 4.0 grains for a 100 grain bullet.
Unless you have some European police pistol from times past, I don't think you can get a bullet larger than the 100 grain ones to operate in most 380 pistols.
Hope this helps,
Jerry