[Unclenick]

In .223, specifically, Charles Petty published some tests in Handloader in 2006 using a 55 grain V-max and 24 grains of Reloader 10X and got velocity to vary from 3150 to 3000 fps by changing primers. That's about the change 4-5% more powder would make. In larger cases using large rifle primers, I've not seen as much difference. Use the search function to find a post by member Slamfire a year or two ago which had some velocities and extreme spreads for different primers, though these were all for .30-06 in the M1 Garand, IIRC. Still, it gives some vague sense of what can happen.