Its realy easy all you have to do is lie !!
No in realaty I have never gotten the published velocity out of any Weatherby factory ammo thats with a 257 , 270 and 300 Wby. I'm not sure if they are just fudgeing the data or if their have fast barrels. here is what works in my Mark V , 1-10" twist 26" barrel
85gr of IMR-7828 = 3130fps avg
86gr of IMR-7828 = 3196fps avg Most accurate but hot load
88gr of H-1000 = 2992fps avg , good accuracy
89gr of H-1000 = 3032fps avg , not as accurate as above.
All loads were seated out as far as the magazine would allow , not sure but I think that all of these loads are close or above max from the Nosler #5 book so start low.
My most accurate load I have found to date has been with the new 200gr Nosler Accubonds
84grs of IMR-7828 = 3041fps avg , warm load , very accurate
82grs of IMR-7828 = 2966fps avg , no pressure,very accurate
88grs of H-1000 = 3022fps avge , no pressure , comperssed
Most accurate load
All these were made up in fire formed neck sized Winchester brass all loaded with Fed 215M primers and seated out as far as the magazine would allow.
Personaly the 200gr accubond would be my choice for anything in this rifle , its an accurate bullet , will expand at all velocities yet retain enough weight and power to give good penitration on a big bull even if the angle wasen't perfect. I did some testing with the 130gr TSX at high velocities a while back and diden't care for them to much they just diden't offer the expansion that I wanted , I fear that at a reduced velocity the heavier ones woulden't open much at all.