This is a ballistics for dummies question with me being the idiot. How will a 20 mph wind from the WNW affect this bullet when I'm shooting from the west and using a 16 inch barrel at 100 yards.  I'd like to know how far "off" of center will the bullet go?

If you estimate around 2200-2250 fps for the round with a .33 ballistic co-efficient, any calculator can spit out a result that will estimate whatever windage parameters you set. I prefer JBM ballistics.

You're talking to a bonified ballistics  and math idiot (me) who never made it out of "math for dummies" class in high school/college. How far "off" of center .300 blk bullet be if shooting in a 20 mph wind?

You don’t need to be doing these calculations yourself, I have no idea how to do that either. Download an app, or visit a website calculator, and input the values. I like iSnipe as a good value app on my iPhone, but there are several I’ve used and that work well.

ETA: I used the aforementioned app and their stock data for 123gr Remington MC (they didn’t have magtech, and I don’t know how accurate Remington’s stated values are, so YMMV and all that). Assuming a 100yd zero with no wind, @200yd w/ full value 20mph wind, it reads 13.7” or 1.9 mils.

Download an app, they’re pretty intuitive and easy to use.