Originally Posted by Vincine
Okay, this is getting to it. But it makes my point. Being off by a hundredth of an inch, or thousandth of a psi, or whatever, on a rifle is a much lower variation than the same variation on a 22lr round and that different lots of 22lr, and even different rounds of the same lot, are more variable than different barrels. So that to say a rifle 'likes' Elmer Fudd brand ammo in their wabbit wifle the best is naive.
No... It's not naive. Elmers rabbit rifle WILL like a particular ammo... but it won't like it forever. How's that for another wrinkle. Not only do we get to deal with finding the right match. We must also recognize that once found... barrel wear with each round fired means it will only go downhill from there.
The best term I've found to explain ^^THIS^^ is "harmonics".
Stick you index finger straight out... Now rotate it as though your drawing a small circle in the air. This is what your barrel is doing while each round travels down it's length. Accuracy is factor of consistently getting your round to exit the barrel at the exact same point of rotation.
^^THIS^^ is why many match grade bench rifles sport "heavy" barrels. While a barrels rifling is emparting "spin" on the projectile, the projectile "and the force of gas pressure behind it" are imparting torque on the barrel causing this rotation and heavier barrels rotate less than light weight barrels.
It's also why serious centerfire competitors use handloads and why rim fire competitors individually weigh each cartridge. Consistency of load determines consistant "rotational" point of exit.
As to why different barrels from the same builder and model prefer different loads, this is a factor of tooling and raw materials. Each time a barrel is "cut" the act of cutting imparts a degree of wear on the tooling, which means no two barrels are ever the same... and different "runs" may come from different batches of steel which effects "harmonics" and the resulting effects of "rotation" and "point of exit.