I use imr 4895 (had it on hand) with 39 gr sierra in a t/c venure with good results. You should be able to find good loads with it. The h335 and blc-2 should work as well.

243 with 95 gr accubond or partition would be good. Your 280 rem with 140 ballistic tips or accubonds would be awesome. Mine puts either bullet in little bitty groups.

39 gr sierra, imr4895, rem 7 1/2. About 15 mph breeze from 10:00.

rem 7 1/2, sierra 39gr bk, 27 gr imr4895, hornady brass, oal 2.315. Shoots under .4" out of my t/c venture. I believe it is a 1:10.

Hornady brass, sierra 39 gr. bk, 27.0 imr 4895, rem 7 1/2 primer, oal 2.315. .316 group