Faster twist needed for heavier bullets, less so for lighter ones like the 40 grainer's.

Original sporters in .223 had 1-14" twist barrels like the .22/250, but as more and more guys started using the longer match bullets, and the military started using heavier than 55 grain bullets for different applications, the twist has gotten faster. I remember when my Mini Mark X which had a twist rate of 1-10" was considered fast. Now....

I'd say that your twist should work pretty well with up to 60-62 grain bullets at normal velocity, and will definately work well with lighter weights as long as the barrel is a goodun'.