Here's 2 rounds that some say are interchangable and others say thier not . I just bought an 1968 Lee Enfield 2A1 ( which is a No.1 Mklll thats chambered for 7.62nato ) . My question is , whats the difference in release pressures between these rounds ?

If I remember it right the 7.62 is loaded with powder of a burn rate to produce the right pressure at the gas port of a semi or full auto rifle to make it fuction properly .To fast burn rate and the pressure is to high ,the bolt may work to fast or bend oprods . To slow an not enough pressure to work the bolt. Also 7.62 is loaded with a narow range of bullet weights from about 147 gr to 180 gr. The 308 is factory loaded with bullets from 55 gr accelerators to 180 gr at least. In a bolt gun IMO you can shoot any bullet weight and any safe burn rate powder .