My way of thinking with regard to the twist rate:
If you send a bullet down a barrel, and cause it to rotate (which is the purpose of the twist), the lighter the bullet for the same amt of powder, the faster it will travel down the barrel, and the faster it will spin.
If you load a bullet that is recommended for 1:12 twist (I have some 32 grain .22 diameter bullets which should only be loaded in 1:12 twist) in a 1:9 twist barrel, they will be spinning so fast when they leave the muzzle (in some cases better than 200,000 RPM's), that they will centrifugally fail in flight. Even the copper shell won't keep them together well.
Exaggerating to make the point, if you took the same bullet as cast (presuming you could make as cast bullets go that fast, which you CAN'T), it would be spinning so fast that it would fly apart into shrapnel virtually as soon as it left the barrel.
I have taken some liberties I know with my example. Don't chop my head off. I just wanted to put it in some terms that you could visualize.
Just as there is a minimum flight rate for a given bullet weight (so that it's dynamically stable in flight), there's also a maximum centrifugal spin rate.
And, that has everything to do with twist rate of the barrel, bullet speed, and bullet weight for a given diameter.
Always check with the bullet manufacturer in any of those cases where it's close. Just the fact that you are asking the question in the first place tells me that there's a potential issue. The bullet manufacturer will advise you IF it's OK to do what you are thinking of doing.
The aforementioned is with regard to lighter bullets in faster twist rate barrels. IE, doesn't answer his question, but touches on an adjoining subject.
With regard to powder use, with an otherwise reasonable powder, keep in mind that some reloading data books are written with bolt action guns in mind. Most of those have a longer twist rate (1:12 instead of an AR style 1:9). It's the reason to have on hand and use sveral sources of current data for your reloading.
And, as has been pointed out, the ULTIMATE source for the powder questions rests with the powder manufacturers.