Thread: Rabbit holeing with primers

I went out to the range yesterday and shot a bunch of rounds through a chrony, I was testing the speed and characteristics of 3 types of primer.

CCI 250 ( Magnum large primer ) MLRP
CCI 200 ( Standard large primer ) LRP
CCI 450 ( Magnum small primer ) MSRP

I had read a lot about them being different and not different so I was going to make my own conclusions.

In my rifle I found there to be a change in velocity from Large to Small primer of about 40 fps. So that is to say that the LRP's went faster than the SRP's

To drive the SRP's to the same speed requires seating deeper, for every 20 thou deeper they were seated I gained 20 fps.

Or you could achieve it by adding more powder ...but thats a different warren on another farm.


With the two LRP's I found the difference in speed to be negligable, but by using the Magnum primer the ES (Extreme Spread) was much lower.

I imagine results would be different for different powder types ( I was burning ball powder under the test of LRP and MLRP ) so that may be why the spread was so low, but it leads me to the conclusion that the only difference between the two CCI primers is cup thickness not compound heat/amount.

Between the LRP and the SRP there is a small advantage in Extreme Spread with the small primer and that is traded off against the seating deepth or increase in powder charge (which ever way you go).

Let me know what your results have been.