Whisper subsonic powder options

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I have been trying different powders and loads for the last few months and have had a ton of fun doing it. Being an engineer, it is in my nature to always look for a better way. With that being said, I have some loads that work pretty good but am looking for more testing and trials..that is part of the fun, isn't it?
I have tried
AA9- does not work in my gun
H110-works ok but but needs some development, pretty finicky
4227- works awesome
1680- works totally awesome
322 works better than H110 and looks promising
Looking at the powder burn rate charts, it appears that my optimum burn rate is between 76 and 100. (of course, just a general observation and by no means substantiated and know that many other factors need to be considered). 4198 falls into this area.
Question: Has anyone tried 4198 for subsonic loads in an AR with a 10.5" barrel? (240,220 and 208 gr bullets)
I have found some load data for RL no. 7 that works for some people, but have found no data on 4198. How about WW748? Anybody tried that?