Originally Posted by Adam
Barrels can have microscopic burrs and jags on the rifling. Most likely at the edges of the barrel lands. These can tear away tiny bits of lead from the pellet edges. As the barrel gets "shot in" or "leaded up", these burrs build up a layer of lead in front of them which makes the barrel smoother to the passage of the pellet. If the burr is too big, the accumulated lead can occasionally get dislodged. This can lead to an otherwise good pellet being an unexplained flyer. The sort of flyer which is close to the group's centre but can spoil a stellar group.
I'm wondering if the mechanism that causes many flyers is a the tiny net change in CoG caused by lead being dislodged by many microscopic burrs which may not be evenly distributed around a barrel. We all know of the existence of "good" and "bad" barrels from the same manufacture possibly from the same manufacturing batch. Maybe this is one cause.
This theory suggests that hammer-forged barrels like the barley twist may have fewer burrs than button-rifled barrels. This may account for these barrels' legendary reputation for being pellet unfussy and needing little or no cleaning.
The Walther dommy barrels seem to have a similar patina to the barley twists on them... so could be something in it. If anyone wants to loan me a barley twist i'll put it through it's paces...