I went through 3 barrels on mine first two were 28 and last was 30. You are talking about short barrel like 400 rounds and case life. So it's best to zoom in and perfect one round. US 869 has the velocity with less pressure easier on the cases. I chose to perfect 220 grain. I didn't have the twist for 240's early on I dabbled with retumbo and these 210 hunting rounds. real elk medicine on loan for out of state hunts.
I just bought lots of kegs of 869. Just when the last barrel had about 500 rounds and was in need of a new one I had planned on up grading to 338-378 to double the barrel life. Reloader 33 had just come out and it was promising according to the 30-378 crowd.
When you look at the burn rate chart, you have limited choices of the slowest powders.
I just set my electronic measure to 120 grains of 869
and it's not a compressed charge. It's very impressive shooting in low light conditions.