I do agree never know unless you run those loads over a chronograph.
When the 300WSM first came out member in our gun club purchase two of them plus case of win 180gr ammo. He just doesn't have the time to reload and he has the money.
We all offer to run his ammo/rifle over our chronographs with he did and he was little faster than published velocity at that time. When Tikka came out with the T-3 in 270WSM he got one of those plus case of ammo win 150gr he was in the high 3100fps with it.
My Kreiger barrel 300WSM was a 2005 270WSM in it's other life never tried factory in that rifle.
I would think your pretty close to factory velocity but my experience is based on those older WSM not the new ones. I had one 270WSM build pretty nice rifle.