That sound you hear in the distance , is the ghost of J.D. Jones screaming about his .338 Whisper being ripped off just like the .300 Whisper !
A subsonic .338 with very heavy bullet is an interesting concept . Albeit a Very Niche concept unlikely to achieve commercial success . But the ripped off .300 Whisper aka Blackout did achieve market success , so it's not a crazy idea to make a speculative stab at bigger bore ctg of similar general concept . This one probably won't , but it's innovative capitalism at work . Invest in speculative R&D , and hope for a big- ish pay back if they get lucky .
To the extent that there is a potential market for a medium large bore subsonic , suitable for autoloading arms , it already exists , and in use since the 1980's , albeit all but unknown in this country .
The 9 x 39 . Somewhat oversimplified , visualize the 7.62 x 39 , necked up to .35- ish ( .366)with 250- 275 grain projectiles .
If you're going to change anything for the US market , change the bore size from .366 to .358 . Shouldn't be too difficult to develop a super sonic loading with +/- 200gr , at a level exceeding the .351 WSL , approaching the .35 Remington .
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Still a niche cartridge , but with significantly more general appeal than the ill fated and largely forgotten .30 AR from Remington . Heck , a good name would be .35 AR .