When working up a load be sure to use the same lot of brass if you can. For example I used the same load 54.5 grains IMR 4350, cci 200, 130 Hornady Interlock in 3 types of brass. I used my Oehler model 33 for load info. The results were;
Winchester brass vel. 2928, es47, sd17
FC brass vel. 2955, es63, sd21
RP brass vel. 2980, es38, sd15
The same load, same day using Nosler BT and FC brass vel. 2945
The Hornady bullets all grouped near 1.5 inches and the Nosler grouped at 1.25 inches.
So brass does make a difference due to the internal capacity from lot to lot and brand to brand.
The rifle was a pre war model 70 with 24 inch barrel.
Good luck,
Dan