Regarding deer legal rounds that are subsonic,
In Scotland (gods country btw) this is not possible despite energies as all rounds must be fasdter than 2450fps.
In England it could be possible in the following circumstance.
410 gr bullet travelling at 1050fps gives 1003lbs of muzzle energy (legal for MJ and CWD)
700gr bullet travelling at 1050fps gives 1713lbs of muzzle energy (ok for all)
Subsonic .50 cal deer shooting anyone?
This math was done quickly back of a fag packet (actually a beer mat), perhaps someone could check this.
regards
DTA