The differences are substantial. I have found that some of the most consistent is Privi Partizan,Seller & Bellot,and Lapua.
I sort my brass by weight. Win,Fed,Rem,Hornady,etc,etc. And different chamberings . . . 308,243,223/5.56,etc,etc. If the weight of different brass is within 2%,I use it. No matter the headstamp.
Of course I trim to length,chamfer the mouth,deprime,square primer pocket,debur flash hole . . . then weigh on a digital scale.
The name of the game is CONSISTENCY. --- SAWMAN