Here's the test results

on the subsonics.  

Standard Disclaimer applies.

Chrony was ten feet from the muzzle, velocities in feet per second.  Both tested out of AR pattern rifles with 16" barrels.

First, two loads in .300 Blackout:
200-grain Berry's  over 11.7 grains CFEBLK
1005
1091
989
1062
1053
avg. 1040

Second, 190-grain boattail hollowpoint match bullet(probably Sierra Matchking) over 10.5 grains H4198:
917
884
941
886
915
avg. 908.6

The 190-grain bullets do give better accuracy at 100 yards, at the indoor range of 30 yards there's barely any difference.


The other loads were 7.62x39 using the same 200-grain Berry's .308 bullet as the first .300 load

12.8 grains CFEBLK
966
1037
954
996
970
avg. 984.6

12.9 CFEBLK
991
997
1016
1004
1019
avg. 1005.4

13.0 CFEBLK
1000
1163
1024
1001
1022
avg. 1042
The second had a definite stronger sound, can only suppose that the measure dropped a touch more powder on that one for some reason/somehow.  If I test these again I'll weigh each charge just to be certain.