For the 300 I'd try rl22 with 165(78 gr.) or 180(75 gr) grain bullets or h1000 with 190's in win brass with a 215. For your 280 ai, I don't load for that one(see log in handle) but my brother uses rl22 with 140 noslers and it is great in his regular 280. With only a few percent difference in case capacity, it should be great in the improved too.
thanks i got the 280shooting 140's but i can't get it to group the 168's.i will statr with the r22 for the 300
I'd still think of rl22 with the 168's in the 280. Retumbo may be another choice if you will put up with a compressed load; it is the fastest of the h powders on their data with a 168.
I've been using rl22 with a 300 win for 15 years and I've done a lot of killing with the 165 hornady with it.
I like I 4350 for accuracy and have burned a few pounds of 4350 in my 300 win, albeit many moons ago in another rifle. I got better speed and similar accuracy with rl22. Some swear by(probably swear at too) rl19 in the 300 win with mid weight bullets. H 4831 is always a classic way to go too. I'd love about ten kegs of h4831 war surp powder. I've only gotten hold of 1 pound and it was better than current h4831 as far as generated speed for pressure. The new stuff was 100 fps down with 180's in another 300 I used to have compared to war surp 4831.