I remember reading where Hornady & Federal's light magnums achieve their velocity boost thru a special mix of powders that dont actually increase pressure, rather they prolong the pressure curve. Normal powders are at peak presssure for a relatively short period. These fancy powders retain peak pressure longer, therefore they push the bullet harder longer than standard powder. Thats why they warn against using them in semi autos. The pressure would be way too high when the bullet passes the gas port & I'd imagine it would get exiting.
Theres really alot more to loading & developing loads than most people realize.
Very interesting actually.