I had always thought this effect was "negligible", meaning don't try to compensate for it in the scheme of other minor variables.
Definitely not negligible. Check out ballistic.zdziarski.com
Jonathan knows his stuff his program uses the JBM ballistic engine, but only
runs on iphone, ipad. You have to turn this option on and select your bullet
profile, he has a huge built in database. Be sure to also enter your rate of
twist, RH or LH, and the length of your projectile.