Got to the range, (first update) Second update, and another bit of 'what I did'

and was able to set up the chrony for those subsonics.  Update with details later.

Part of the update:
I had two sets of five loads, both using the 200-grain Berry's plated bullets.  Five used Federal cases, five Lake City that had been converted to .300 Blackout, both with the same load-

DISCLAIMER

I started with the load in the new Lyman manual, and worked down .1 grain increments.  Note that the manual says "DO NOT REDUCE LOADS", as, if you get it too low, you could wind up with a bullet stuck in the barrel, which can rate from 'a pain' to a big 'Oh SHIT!'  And yes, I was very damn careful trying these loads.  If you use this, the results are on you.

- which I'll tell you if you ask in the comments, at 50 yards.  Time came to try them, I discovered I hadn't brought the rest bags I use with AR type rifles, so didn't have the best of rests.  Both were about equally accurate, but the velocities were interesting: 

Federal cases        LC cases
    1000                    914

    1081                    928

      985                    943

      973                    933

For some reason the LC cases gave much more consistent velocities.  As to accuracy, 

the two at the bottom are with the Strike Eagle center dot centered, and the Federal cases.  So I used the first stadia line as the aiming point for the next three, which are the three up/left.  Then used the same aiming point with the LC cases.  Considering the rest, and that this was at the end when the cool and wind was getting to me I won't say "THIS one is the best!" until I can try both again.

Thus ends the first update.


2nd Update:

Also tried some .45-70 loads, and this one looks real promising

Promising because the first two were on top; the third I knew I'd pulled as soon as the trigger broke, that's off to the left.  Fourth was right in with the first two, and the fifth, I'm pretty sure was my fault as well.  So this one I'll try again.   Difference between previous results with this load?  This was with Winchester cases instead of Starline.  We'll see if this works with the next set.

Yes, there were some others; none worth getting excited about.

'What I did'
with that warning about reducing loads in my mind, when I started working with reducing it I made sure I had the 36" brass rod along.  I'd fire one, make damn sure that
the bullet hit the paper, and
the hole was round.  

And kept looking at both with each shot.  The rod was in case one didn't make it out of the barrel.