Heavy bullets don't only translate into round nose.
PeeWee and I are making 150 grain and 168 grain bullets by merely adjusting the weight of the lead cores. I could easily make 180 or 200 grain bullets with the same dies in .308" diameter by increasing the lead cores yet again. Anything over about 175 grains will have exposed lead noses, and BT Sniper has previously shown images of those.
Bottom line is that you don't need RN bullets to stay subsonic. Just heavy.