I do not have a quarter bore, so my experience there is nil. But in general the longest bullet that will stabilize will work best. I said in general, because there are exceptions to every rule - some times lots of exceptions. The reason is that the slower the bullet spins, the more accurate it will be (as long as it is stabilized). The faster a bullet spins the more a slight defect in the bullet will throw the bullet off of the true flight path. Of course a heavier bullet needs a faster twist rate to stabilize, but it is heavier so the velocity is down - thus reducing the spin rate (in time, not distance)). For instance - in a 223 if you are going to shoot light bullets (52 grain and under) you will be better served with a 1 - 14" twist. If you are going to be shooting 75 grain bullets, you will need a 1 - 8" twist to stabilize the bullet, but is shoots at a much lower velocity so it will not spin as fast (per second, not per yard) as say a 45 grain bullet in a 1 - 8" twist. Any defect in the 45 grain bullet will be magnified due to the faster spin rate. Like I said this is in general - there are always exceptions to the rule.
