I find no I4166 data for the .250 Improved, but with published data of 39.4-43.8gr for 75gr bullets in the .257 Roberts I shot 38-40gr with the 70gr Blitz-king. Most accurate was at 38gr for 3160fps (19fps ES for 5 shots) while 40gr gave 3328fps (40fps ES for 5 shots).
40gr of CFE223 was accurate in my rifle (700Rem) at 3225fps so I've now got a couple copper cleaner rounds in that velocity range. I've already got accurate loads at 3480-3510fps using R15 and H4895 with the 70BK, so won't be pushing the new powders any higher.
Hodgdon's booklet shows 28.1gr of 4166 as a max in the .204 Ruger with Berger's 35gr HP, and in my Ruger's 24" bbl 28gr was good enough at 3744fps and 4 shots in 1.4" at 200 yards. I've gotten similar speed and better accuracy with CFE223, but 4166 could work.
In the .270Win the search is for light recoil with light bullets and enough accuracy to hit silhouettes at the shorter ranges of 200 and 300 yards. I found something good for Hornady V-Max 110gr at 2960fps and Sierra 90gr HP at 3140fps. The lighter end for 140gr bullets was too light at 2660fps, so next up will be increases to get them over 2800 and see where accuracy is best. Not that it will be critical, my misses at high power silhouette are more indian than arrow.
