11 tw barrel ???6.5x284 is hard on barrels and you want to try a double base powder through a smaller hole? I would be tempted to try H1000 with heavier bullets, as it is cool burning.
I have a 11 twist 6-284 and have been using 4831 & H100v but was wondering bout R17?
RL-17 would be WAY too fast. It is optimum in 6Dasher. I recommend trying RL-26. It is in the appropriate speed range and is the only Alliant other powder besides RL-17 made by Nitrochemie of Switzerland. You can read all about their special properties in the archives of this website.
Using either of these powders has been documented on another website as virtually doubling barrel life, because much of the "burn" occurs beyond the throat.
He has a 11” twist barrel so he will not be shooting heavies requiring a slower burn rate powder. Re 17 will work fine for the class of bullets he will be limited to shooting.