OK...... there is a real reason for neckturning but ONLY if your parent brass is fatter than your chamber neck, by plan. A long time ago experimenters realized that bullets don't just slip easily into the lands of the rifle. Instead they're forced in with a 600lb hammerblow, a swirling, whirling turmoil of gas and particles and tremendous pressure which JAMS the poor bullet into the hole with the lands tearing and crimping at the jacket, causing the lead to flow like water and gener'y buffeting the beejeebers out of the wee beastie.
For this to all happen properly the cartridge case must first and foremost do the job for which it was designed and developed.
That of a GASKET.
The cartridge case is a GASKET, it ain't just a convenient way to carry powder and ball.
For it to work as a gasket it must gask properly which means that as the pressure builds it LETS GO OF THE BULLET and opens itself up to plaster itself against the chamber/neck walls. And it works. It works well..... generally only a small bit of the gas finds it's way around the end of the neck before the case is tightly sealed, ironed against the walls of the chamber. Some handloaders get to experience what happens when too low pressur buggers up this process and the case DOESN'T seal up properly......... "pleated" cases, staining and wrinkles all down the sides and maybe even a blast of gas.
WEAR THOSE SAFETY GLASSES CHI'DRUN!!! God gener'ly gives ya' one fer free but that's no excuse!
So anyways, the neck opens up to seal the system and the bullet's just hanging there with it's hindquarters in the breeze. And it's quite a breeze, building to near a gale before that bullet starts ripping it's way into the rifling lands....Ain't no neck ON IT..... In other words the bullet WILL be slammed up against one side or the other of the neck, randomly. ALL bullets under ALL conditions. And said bullet will maintain that attitude (only worse, picture 600lb and building pushing against a bent-over bullet) all the way to the target. A loose neck leaves the bullet with a built-in cant (it's often termed in-bore yaw) as it travels down the barrel. This built-in cant coupled with 200-300,000rpms rotation leads to inaccuracy.
Hence turned necks.
Turning necks originated as a way to lessen in-bore yaw. You still need some clearance so's you can get the round in but generally speaking, it's a truism that less clearance equals less cant on the bullet, less in-bore yaw. "Tight necked" chambers were developed to give the use a way to play with this clearance. A tight neck and a tight freebore act to keep the bullet as straight as possible whilst it's HAMMERED down the pipe.
Turning necks on already large-nekkid chambers is like adding more grease to a burnt out bearing hoping it'll "take out some play on the shaft..."
opinionsby
al
