What caliber, what Bullet, what powder? I can look it up in several loading manuals, but when he answers, can someone share legit data from a manual?
Suggestion, hit a couple 300BO reloading forums and snoop around.
300BO especially subsonics are an odd duck.
In the old days if you looked at reloading say 30-06 150 gr. and you looked at six different manuals they would all be pretty much the same.
Now days with cartridges like 300BO they are very different and when you get to subs they are so wildly different they will scare you or at least make your head hurt.
one says h110 max 8.5 another says 9.7 and another says 14.2 well there's no way there can be so much difference, so I watch forums to see what they say.
Especially the guys who post chrony results, bullet groups, and their recipe.
300BO especially subsonics are an odd duck.
In the old days if you looked at reloading say 30-06 150 gr. and you looked at six different manuals they would all be pretty much the same.
Now days with cartridges like 300BO they are very different and when you get to subs they are so wildly different they will scare you or at least make your head hurt.
one says h110 max 8.5 another says 9.7 and another says 14.2 well there's no way there can be so much difference, so I watch forums to see what they say.
Especially the guys who post chrony results, bullet groups, and their recipe.
Just seeing this thread for the first time. I've been reloading for almost 40 years, but have only reloaded subsonic in the last couple years, and for only the .300Blackout out of a bolt action Remington. Some things that are different imo and something I had to get used to was that I was looking at max velocity and accuracy almost exclusively for subsonic and not max pressure. Pressure and reading my cases along with accuracy was what I always focused on with supersonic. I've reloaded subsonic loads with such little velocity and pressure with the .300blackout that the bullet didn't leave the barrel, and I could hear the gas escape when I opened the bolt lol. These were powder charges not far below the "max subsonic" recommended loads with some powders. Shooting thru a chrony every time when working up subsonic is necessary imo, both for subsonic noise purposes and safety. When you squeeze off a "zeroes" shot on the chrony, better double check your target and barrel and be ready to push your bullet out 
I've not tried to tackle the semiauto subsonic game where it needs to remain subsonic and still have enough pressure to work the action properly.
I've not tried to tackle the semiauto subsonic game where it needs to remain subsonic and still have enough pressure to work the action properly.
CFE Black has data from 110gn to 230gn. The trick would be after 180gn there is no start just a max so you would have to play around with it and check your brass ect. The supers all have a 2-3gn of powder variance from start to max so you could logically apply the same logic but it will ultimately come down to your gun and your set up. Hodgon shows a max load of 11.6gn cfe black with a 208gn A-max listed at 1041fps. If you follow the typical spread of powders you could start around 9gn of powder and work to max verifying hit on target and proper cycling of the action. These are theories and not facts so do your research and testing. I haven't gotten into subs yet but it is on my list.
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