When comparing two 30 caliber cartridges in different barrels for muzzle velocity, ensure both barrels have the same bore and groove dimensions. Their pressure should be at SAAMI specs and both rifles held and fired the same way. The same bullet should be used in both cartridges.
The best source of data comparing two rifle cartridges is SAAMI's documents listing pressure and velocity values. The "Rifle" link in:
https://saami.org/technical-informat...mber-drawings/