Ask Cecil, last i heard his response was. "There is a reason they call it 209".

BUT....

Ive heard from several people that some of the ACP conversions work fine, although i have no idea how cold of weather they have used them in either. A friend with a converted T/C swears his is flawless with BH209. He opened up the flash hole in the brass or so he claimed. I would like to see some hard data on this too and with variations such as the 6mm/LRP case conversion. Ive used WinT7s with BH209 without an issue in a well designed BP but they are twice as hot as a SPP or SRP.