Coincidentally, there's a parallel discussion going on in the NationalMatch forum. Here's about the most cogent and detailed analysis I've seen to date;
http://bryanlitz.bravehost.com/EpSwerv.htmlI had the opportunity to pose the question about grouping smaller at longer range to distinguished Ballistic engineer, William C Davis Jr, of Tioga Engineering. He just wrapped up an incredible career doing work for outfits like Aberdeen with sidelines as a technical editor for American Rifleman. He's also the designer of the VLD bullet (Very Low Drag). In our conversation, he essentially asserted what Brian Litz says in his article. The "corkscrew" path is actually quite small (he introduced me to the terminology "swerve", and in all his work, had never seen the phenomenon in a controlled test.
What impressed me was that he didn't flat out reject the existence of the phenomenon, but just said he hadn't ever seen a well documented case of it. During the course of our conversation, he proceeded to think out how he would conduct an experiment to document the phenomenon using thin paper targets at various yard lines. Others since have extended that line of thinking proposing acoustic targets to further prevent disturbing the flight of the bullet, yet documenting the groupings at the various yard lines.
