I happened to look at the muzzle of my .22 caliber Diana 54 one day and noticed that the rifling was different from what I expected. Instead of being a series of narrow ribs that would engage the pellet and impart rotation, the rifling consisted of a set of narrow grooves, leaving the pellet riding on almost the entire circumference of the bore. Because I was curious how much pellet engagement would be provided by the narrow grooves, I shot a pellet from the Diana and another from a .177 TX200 having conventional rifling into water. Here is the photo.
As you can see, both pellets appear to be contacting only the lands, with very little if any contact in the grooves. This creates a situation where a pellet shot through an Air Arms barrel is riding on less than half the bore circumference, whereas a pellet shot through a Diana barrel is riding on 4/5 of the bore circumference. Note that this is partly the result of the AA barrel having 12 grooves, while the Diana barrel has only 8. Is there any significance to this difference? Is there some reason to believe that one type of rifling would be more accurate, or maybe more tolerant of pellet fit? On the manufacturing side, cutting narrow and fewer grooves would remove less material and perhaps result in a less costly process. Other than that, I don't see an obvious advantage to the Diana configuration.
However, engagement and resulting displacement of 4/5 of the pellet diameter might explain why the .22 Diana has a reputation for being sensitive to pellet fit at the breach. Too small a breach diameter might result in a pellet that is hard to seat, forcing Diana to choose a breach diameter that is just small enough to hold most pellets in place with the gun vertical.
Any thoughts?
As you can see, both pellets appear to be contacting only the lands, with very little if any contact in the grooves. This creates a situation where a pellet shot through an Air Arms barrel is riding on less than half the bore circumference, whereas a pellet shot through a Diana barrel is riding on 4/5 of the bore circumference. Note that this is partly the result of the AA barrel having 12 grooves, while the Diana barrel has only 8. Is there any significance to this difference? Is there some reason to believe that one type of rifling would be more accurate, or maybe more tolerant of pellet fit? On the manufacturing side, cutting narrow and fewer grooves would remove less material and perhaps result in a less costly process. Other than that, I don't see an obvious advantage to the Diana configuration.
However, engagement and resulting displacement of 4/5 of the pellet diameter might explain why the .22 Diana has a reputation for being sensitive to pellet fit at the breach. Too small a breach diameter might result in a pellet that is hard to seat, forcing Diana to choose a breach diameter that is just small enough to hold most pellets in place with the gun vertical.
Any thoughts?
