The Firing Line Forums - View Single Post - Neck sizing vs FL- bolt pros and cons

Bart B. · October 10, 2012, 05:37 PM

Virtually all the high power match rifle matches are won with and records set with full length sized cases.

Sierra Bullets tried all sorts of fired case sizing tools and techniques in the early 1950's; they've used full length sizing dies since. These days, they use Redding full bushing dies with bushing diameters a couple thousandths smaller than a loaded round's neck diameter for ammo those dies are made for. Redding standard full length sizing dies for all the others. Fired case shoulders are set back no more than a couple thousandths. I doubt anyone gets better accuracy with their bullets than they do. So sized, their test cases produce sub 1/4 MOA accuracy with their best match bullets. . . .at 200 yards. And with metered (not weighed) powder charges in unprepped cases, too. I've seen sets of Sierra's quality assurance test targets with all the 10-shot groups under 2/10ths MOA shot with Sierra 30 caliber 168 grain HPMK's.

Benchresters have been moving to full length sizing dies for some time. Not a surprise to me as full length sizing dies center the case neck more perfectly on the case shoulder. As bottleneck cases center their shoulder in the chamber shoulder when fired, the case neck darned well better be perfectly centered on that shoulder else it'll be off center. . .and therefore so is the bullet to the bore. The case neck floats in space somewhere in the chamber neck; it ain't supported by anything except the case shoulder.

The smallest series of 10- or 15- or 20-shot groups ever fired at 600, 800 and 1000 yards I know of have all been made with cases resized with full length sizing dies; bushing ones for the most part. These aren't benchrest records; just tests with machine rested (normally shoulder fired) match rifles and their ammo.

Set the die in the press such that bottleneck case shoulders are set back only 1 or 2 thousandths. Use dies with the correct neck diameter so no expander balls don't need to be used. Fired case body diameters need be reduced no more than a couple thousandths; more is ok but case life may be less.

Properly set up, full length sizing dies will get a few dozen reloads on .308 Win. cases. Some folks have got several dozen.

Many folks get better accuracy with new cases than any fired case neck sizing tool or process for fired cases. Done right, there's little difference between new and full length sized cases.

It's a common belief that neck sized cases fit the chamber "perfectly" or "concentric" better than full length sized ones. 'Tain't so. Here's why......
After closing the bolt on a bottleneck case that headspaces on its shoulder, the case extractor pushes the back end of the case up or sideways such that the case body at the pressure ring (about 2/10ths inch forward from the case head) presses against the chamber at that point. The back end of the case is never centered in the chamber with the bolt closed on it. Up front, the case shoulder's pushed into the chamber shoulder by in line ejectors and very hard by firing pin impact well centering the front of the case in the chamber at that point. If the case neck ain't well centered on the case shoulder, it'll be off center in the chamber. As there's no such thing as perfectly round chambers or cases, there needs to be a bit of clearance around the case just behind its shoulder else the out of round points may push the case off center on the shoulder. Consider what happens if you chamber a .243 Win. round in a .308 Win. chamber; it'll center perfectly up front and its neck will float well centered in the chamber neck but with way too much clearance for actual firing.

Naysayers need to measure chambered rounds' position in a chamber and see exactly how their necks center in the chamber neck.

October 10, 2012, 05:37 PM	#9
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Virtually all the high power match rifle matches are won with and records set with full length sized cases. Sierra Bullets tried all sorts of fired case sizing tools and techniques in the early 1950's; they've used full length sizing dies since. These days, they use Redding full bushing dies with bushing diameters a couple thousandths smaller than a loaded round's neck diameter for ammo those dies are made for. Redding standard full length sizing dies for all the others. Fired case shoulders are set back no more than a couple thousandths. I doubt anyone gets better accuracy with their bullets than they do. So sized, their test cases produce sub 1/4 MOA accuracy with their best match bullets. . . .at 200 yards. And with metered (not weighed) powder charges in unprepped cases, too. I've seen sets of Sierra's quality assurance test targets with all the 10-shot groups under 2/10ths MOA shot with Sierra 30 caliber 168 grain HPMK's. Benchresters have been moving to full length sizing dies for some time. Not a surprise to me as full length sizing dies center the case neck more perfectly on the case shoulder. As bottleneck cases center their shoulder in the chamber shoulder when fired, the case neck darned well better be perfectly centered on that shoulder else it'll be off center. . .and therefore so is the bullet to the bore. The case neck floats in space somewhere in the chamber neck; it ain't supported by anything except the case shoulder. The smallest series of 10- or 15- or 20-shot groups ever fired at 600, 800 and 1000 yards I know of have all been made with cases resized with full length sizing dies; bushing ones for the most part. These aren't benchrest records; just tests with machine rested (normally shoulder fired) match rifles and their ammo. Set the die in the press such that bottleneck case shoulders are set back only 1 or 2 thousandths. Use dies with the correct neck diameter so no expander balls don't need to be used. Fired case body diameters need be reduced no more than a couple thousandths; more is ok but case life may be less. Properly set up, full length sizing dies will get a few dozen reloads on .308 Win. cases. Some folks have got several dozen. Many folks get better accuracy with new cases than any fired case neck sizing tool or process for fired cases. Done right, there's little difference between new and full length sized cases. It's a common belief that neck sized cases fit the chamber "perfectly" or "concentric" better than full length sized ones. 'Tain't so. Here's why...... After closing the bolt on a bottleneck case that headspaces on its shoulder, the case extractor pushes the back end of the case up or sideways such that the case body at the pressure ring (about 2/10ths inch forward from the case head) presses against the chamber at that point. The back end of the case is never centered in the chamber with the bolt closed on it. Up front, the case shoulder's pushed into the chamber shoulder by in line ejectors and very hard by firing pin impact well centering the front of the case in the chamber at that point. If the case neck ain't well centered on the case shoulder, it'll be off center in the chamber. As there's no such thing as perfectly round chambers or cases, there needs to be a bit of clearance around the case just behind its shoulder else the out of round points may push the case off center on the shoulder. Consider what happens if you chamber a .243 Win. round in a .308 Win. chamber; it'll center perfectly up front and its neck will float well centered in the chamber neck but with way too much clearance for actual firing. Naysayers need to measure chambered rounds' position in a chamber and see exactly how their necks center in the chamber neck. Last edited by Bart B.; October 11, 2012 at 10:34 AM.