I've just gone through my archived documents and found an article by Robert Beeman. This is a quick cut-and-paste from what he wrote in 2005:
"Also, as is the case in so many considerations of airgun performance, minute differences of various factors, which might have a great effect on airgun performance, might simply be swamped by the relatively tremendous force and projectile mass of firearms. Thus differences which would favor the accuracy of smaller projectiles in airguns may have little or no significance in firearms. We are just starting to understand airgun ballistics, but it is clear that we cannot simply consider them as if they were small firearms. Many aspects of airgun ballistics will surely be shown to be partially or even fundamentally different."