I have found my loads match the claimed velocities in the Alliant manual but my velocities run quite low approx 70 fps behind the Nosler manual. I have found most factory loads are also approx 50-70 fps lower than claimed in my rifle.
Some of that difference is that the Nosler Manual is determined from a 24" barrel and my rifle has a 22" barrel.
For safety reasons the test barrels are set to minimum SAAMI specifications. This runs pressures up and increases velocities. Not necessarily because they are dishonest just better to error on the side of caution. Factory rifle chambers tend to be sized on the generous side to reduce chambering problems.