1200 fps w/ a 100gr is .327 from a snub territory, .32 Mag from a snub is around 1050-1100 fps with premium 100gr stuff like Buffalo Bore, 950 with 80 and 85gr mainstream ammo like Hornady.
The H&R Mag can go as fast or faster with a 33% heavier bullet than what .32 ACP can, yet operates at the same pressure.
What holds .32 H&R mag back is the non boutique ammo companies will load it down to keep them from destroying the original H&R .32 Mag revolvers. I don't think hot stuff like Buffalo Bore would blow up those weak H&R revolvers, they would likely bust the timing and lockup tho.
.32 Mag is a cartridge capable of more power, not max .327 levels, but something around 30k yeah.