As much as I have disagreed with KThomas over the years, I do have to agree with him on this part although I know he is just stirring the pot. I also believe that YoDave and Kt are actually agreeing on the same point that neck turning is more in the eye of the beholder than tangible benefit depending on the level of accuracy required from your sport.
AcrashB you are correct that you need to neck turn because you are “making” a new caliber case from another case and you need to remanufacture the case to correctly fit for safety reasons among other things. I also have heard of “tests” being done but I haven’t read many in print. For example, in Mission, B.C. a benchrester (champion level) tested the amount of neck side clearance in his rifles. He found the more side clearance he put into his rifle chamber the tighter the accuracy became so he shoots large side clearance chambers and wins. Never published but locally known and accepted.
Benchrest is the most demanding of absolute accuracy, F-Class is next and finally a long, long way down the accuracy requirements is the PRS game although some shooters are beginning to understand. Benchrest fires very few rounds in a match and the barrel is cleaned very often so the rounds and chambers mostly are shot very clean. I haven't shot benchrest but I understand the groups under the 1's are required to win. Barrels are also considered "shot-out" after a few hundred rounds.
F-Class matches, on the other hand, are probably more demanding on equipment and ammunition than any shooting sport because matches are long strings of 25 rounds+, the barrels come off the line extremely hot and dirty, multiple long string matches are shot each day and ammunition can be extremely high pressure to chase a node. Yet we demand them to maintain very tight groups through it all and a long barrel life. Winning accuracy standards for rifles is .25 to .3 MOA out to 900 meters/1000 yards else the barrel should be pulled. Barrel life over 2000 rounds for 284’s and 1200 rounds for magnums is about normal.
PRS, on the other hand, have very loose accuracy requirements/standards from my experience and most PRS shooters aren't that skilled in long range shooting at least from my experience being around them. They seem more concerned about buying and wearing high priced gear than shooting accurately. Why worry about neck-turning when you can shoot factory ammo and win.
This leads to the augments like I see above. Benchresters see value in tight chambers and precision fitted components and possible they are right in their game where they only use 5 to 10 cases ever, clean their barrels after a few rounds and reload at the range. I shoot F-Class and take 800 rounds of ammo to a big match. I have also found that tight neck diameter chambers with small neck clearances cause real issues like pressure excursions, blown primers and flyers as the fouling builds up so that now I run large diameter no-turn necks with large side clearances. I also see no need, from my experience, to neck turn, and remember my standard for accuracy is .25 moa at 900 meters after a 25 round string with a smoking hot barrel. I have found that other reloading procedures are more important.
I believe that the game you shoot drives your understanding of requirements so it is counter-productive to ague which is the "better" procedure, turn or no-turn.
From a PRS shooters perspective shooting in a SAAMI chamber at huge targets, why bother.
From an F-Class shooter if you believe it does help then you will. More and more of the guys I know have quit turning because other things help better and not turning saves time in producing large amounts of ammunition.
From a benchrester with a tight chamber so standard brass brass won’t fit then you must.
To argue among yourselves that neck turning is a must and written in stone is fruitless.
I don't have it but only remembered it from years ago. From what I remembered it only showed a very slight improvement (second decimal) on a hunting rifle.
