I am looking for a powder that burns a little slower then red dot but still takes up a good amount of space like the red dot. Ive tried H4227 but doesnt fill the case enough in my mind. Its for a 338 whisper rifle 7mm BR case necked up to shoot a 338cal 300 Mk bullet. will all types of powder get a low ES or some are just better then other. which to look for in this burn rate?