Re: Possible causes of high ES
How many different powder charges did you chrono?
Finding a powder charge with a low ES is the key, and is the biggest determining factor in establishing a good ES.
Also you may want to try US869,( it's a fine ball powder), if you can't get results with retumbo.
Sometimes you can get a powder bridging in the neck of high capacity small caliber cases with large extruded powder and that causes lots of problems, including High ES as well as pressure spikes.