Possible that you are confusing "breech pressure" with something else - is quite possible to create an 90,000 psi load in 308 Win or 7,62 NATO with 110 grain bullets - just use some fast burning powder - like for a pistol round or for shotguns. Can likely produce a 40,000 psi load with 200 grain bullets, again, just select the appropriate powder (if it exists). Breech pressure is what makes rifle come apart - not muzzle velocity or bullet weight.
As per recent threads, also, do not confuse pressure ratings given in CUP units and pressure ratings given in PSI units - not the same thing, at all. Very quite possible to have a particular load with a pressure rating of 40,000 CUP and 55,000 PSI. Also, to make it fun, CIP in Europe and SAAMI in USA measure pressure in different places within the same chamber, so the same load gets slightly different numbers, and for some cartridges, both organizations have published pressure limits using both pressure units - which are not always the same. Then, the British measure pressure in "tons per square inch" and they measure the axial pressure, not the radial pressure...