I am shooting 22-250 how do i know when a bullet is no good for my twist?

When you get really poor grouping or keyholes. Most 22-250s have a 1-14 twist and 55 to 60 grain are about max. Flat based shorter bullets will stablize better.

srose has good info. You can also get some idea of recommended twist rates by bullet weight from these sites:
http://www.bergerbullets.com/Products/index.html

http://www.shilen.com/calibersAndTwists.html

http://www.riflebarrels.com/pr...iber_twist_rates.htm

If it's a stock rifle and not a Savage, I'm gonna guess that the twist is either 1/14 or 1/12. 50-55grs will work well. Maybe a 60gr will work well if it's not too long.
Saavage is more into the specialty twist so I don't know about them.
It's a simple task to determine your twist rate.

It's fairly easy to determine what the twist rate of your barrel is.

Here are a couple ways to do it:

Way 1

Way 2

Way 3

Good luck!