Load data for 300 Whisper, all with 220-gr bullets. altered 221 Fireball cases and Rem 7 1/2 primers, ALL give sub-sonic speed:
AA5 - 7.5 grs
AA7 - 10.5
AA9- 8.5
1680 - 10.3
2015 - 12.0
(I cannot understand the charge weight for AA7, but that powder has always been a conundrum to me - RR)
H110 - 9.0
4227 - 9.2
335 - 13.8
Edit to add: Here's the webpage source of this data
http://www.quarterbore.com/300whisper/