Will a 20" 1:9 stabilize the heavier (77gr?) projectiles?  Will it over-twist 45gr at 3500+fps?  I'd like to shoot Winny white box for plinking fun but also be able to deer hunt (223 is legal here for our dog-sized deer).  If there's a better, lighter bullet for hunting bigger critters I'd like to know what it is, where I can get it and whether or not I can stabilize it, if not what DO I need for twist?

Quoted: Will a 20" 1:9 stabilize the heavier (77gr?) projectiles?

Not likely.

Will it over-twist 45gr at 3500+fps?

Absolutely not.  Most overstabilization is myth.  If it doesnt fly apart, then it shoots.  Might be be "as accurate" but is nothing compared to failure to stabilize.  My 1:8 twist shoots 45grainers at 3500fps plus into very tight groups.

I'd like to shoot Winny white box for plinking fun but also be able to deer hunt (223 is legal here for our dog-sized deer).  If there's a better, lighter bullet for hunting bigger critters I'd like to know what it is, where I can get it and whether or not I can stabilize it, if not what DO I need for twist?

The winny white box varmint does great in a 1:9....  and is great for plinking and varmints.  I would not use it on deer, however... as the bullt will fragment violently with very little penetration.  That will likely work great on a direct heart/lung shot, as long as you have a clear broadside shot and dont hit any ribs/bone/thick muscle on the way in.  If it did, your results could be very unpredictable with such a light round.  For deer with an AR I would choose the Winshester 64gr power point which will also work well in your 1:9 twist.

Was just looking at those.  It looks like 1:9's the twist I need to specify for what I'm doing.

Now for the rest of the project....