And now, a bit on the range

The big try was some subsonics at longer distance than 30 yards.  The first being the .300 Blackout using the 200-grain Berry's plated bullets.  Which proved to be quite nice.

50 yards

The Strike Eagle scope has a central dot with several stadia lines below it.  This was with the dot on the center aiming point.  Yes, I should have tried the first line, but I didn't.  Then moved to 100 yards

For the moment ignore the three at the bottom right.  The one dead center at the bottom was the first shot, using the first stadia line to aim.  Moved to the second line, which moved the group up to about 3" below the POA, with a decent group.  Especially considering the wind.

There was no 200 yard target, because I wasn't up to another 400 yard walk out and back, but there is a gong, about 12" diameter.  Using the bottom line, it was a bit low.  Below that there's a thick vertical post with a sharp point, put the bottom of the gong on that point and I could ring it every time.  Which, for a practice load, is very much good enough.

The other test was of a 7.62x39 subsonic, using the same Berry's bullet.  That idea came from a new load from Hornady using a 255-grain Sub-X bullet.  No, I didn't slug the bore, just put one of the Berry's into the muzzle, and it looked like it'd fit decently until I can find a .310 bullet suitable.
Note: started down this path when a coworker found a company that makes subsonics in this cartridge with, I believe, a 225-grain bullet and he bought some.  And managed to get some .310 bullets in that weight, and worked up a load using CFEBLK powder.  I started with that* and, this being lighter, started with just over a grain less powder.  Which worked, producing a nice group at 25 yards that hit 19" below point of aim.  And very dirty cases from the pressure being low enough that the brass wasn't expanding enough to seal well.

This led to some further test loads, as follows after the 
DISCLAIMER:
I tried these, with a definite amount of "Am I going to screw up this rifle?" as I went.  If you try this, you're on your own.
That said, I started with 12.0 grains, then 12.2, 12.4, and 12.5.  The last gave the best performance, the shots hitting about 2" low and a bit right at 25 yards, but still fairly dirty cases.  That last came out to ~950fps.

I did manage to find a box of the Hornady Sub-X loads to try, and at 25 yards they were a bit low & right, and three shots went into one slightly large hole.  I was impressed.

At 50 yards, 

That vertical string was aimed at the upper right aiming point.  The holes just even with the bottom of the center target came from three of the Hornady.

Remember that group up above I said not to worry about for  now?  That was three of the Hornady loads, holding on the center target

Considering how hard these are to get, and expensive, but mostly because no paper at 200, I didn't try them at that range.

So, for  7.62x39 I'll wait for a more suitable diameter bullet before I load any more of these for it.  the .300 Blackout, I'll definitely load more of those.

* I could find lots of "Well, I tried this bullet and powder" stuff at various forums, but none with 200 or heavier bullets, so guessing game began.