What causes one round to not shoot consistent with the others?
Here's 22 plinkster's tour of the CCI factory:
A lot has been made about the camera capturing them just dumping bullets from one container to the next. I'm using CCI as an example here, but if the bullets are dinged up, each one will fly a little differently. If you had a bunch of centerfire bullets that were all dinged up they wouldn't all fly exactly the same either. Even the better plated handgun bullets are restruck for uniformity.
Rimfire ammo is "consistently inconsistent" by nature. There are so many things that affect it. Here's just a simple list:
Powder - lot number, charge weight
Priming - composition, charge, and uniformity in the rim
Amount of crimp
Brass uniformity - size, thickness, hardness
Bullet uniformity - lead composition, weight, swaging (size and uniformity of the bearing surface), and coating or plating (thickness), care in transportation. Don't forget the rimfire bullet heel. This is something that you cannot see without taking it apart. A person has no idea how uniform the bullet heels are.
Bullet lube - composition, application
And many others...
So we're left with things we can measure, external things weight and rim thickness, and of course velocity.
However, there are over 100 manufacturer measured data points for the best match ammo. Even then, excellent 22LR is a box of 50 with an ES of 40fps or less. Long range shooters would laugh at those kind of statistics. People waste time trying to sort by rim thickness or weigh and sort out the flyers, measuring 2/100 things. Then, they claim some meager "improvement" with a small sample size that could be explained by other factors. It's like when statistics report an increase in the death rates for the elderly and an increase in sales of ice cream cones. Ice cream cone sales didn't cause the death of the elderly. It's because it was a hot summer and they wouldn't turn on the A/C.
Dinged up bullets, uneven bearing surfaces, inconsistent charges, inconsistent priming, et cetera is why rimfire ammo is "consistently inconsistent" and why unexplained flyers still exist.