Cartridge Reloading Accuracy Comparison: Case Neck vs. Full Length Resizing
I have heard that case neck sizing was more accurate than full sizing. In fact, Lee Precision’s guarantee statement for their neck sizing dies is the "Smallest group size or your money back." Another thing that I have heard recommended is to deburr the flash hole. What I started to wonder about is just how much more accurate these steps make your shots. I looked in the three reloading manuals that I have and on the internet, but could not find any report of how much more accurate these methods are. I decided to run my own test. The 100 yard group size test results are below followed by my explanation of the testing and at the end a conclusion.
The following 223 rifle load A and two 308 rifle loads B & C were used for this test.
Load "A" - 223 Remington - 64 gr. Winchester P.P. bullet, 24.9 gr. Varget powder, Winchester Small Rifle primer and Winchester case. Rifle used was a single shot H&R Handi-Rifle. Dies used were by Lee Precision.
Load "B" - 308 Winchester – 150 gr. Hornady SPBT bullet crimped at cannelure, 42.5 gr. Varget powder, Remington Large Rifle primer and Remington case. Rifle used was a Savage Model 14 Classic. Used Lee dies.
Load "C" - 308 Winchester - 165 gr. Remington Core-Lokt bullet crimped at cannelure, 42.5 gr. Varget powder, Remington Large Rifle primer and Remington case. Rifle used was a Savage Model 14 Classic. Used Lee dies.
The cases were prepared as follows. I started with a used case fired from my rifle. The fired case had been pushed out by the propellant gasses to the rifle chamber dimensions. To reload it either a full size or neck die is used. A full size die is run over the full length of the case to give it a little clearance to the wall of the rifle chamber. Also, the neck is tightened to hold a bullet. A neck die just tightens up the neck to hold a bullet. Neck sized cases are limited to being fired in the same bolt action or single shot rifle that previously fired them, since they now may fit only that chamber.
A Deluxe Deburring Tool from Possum Hollow Products was used to deburr the flash hole. This tool has a small cutter that you insert through the case mouth and into the flash hole. You then spin it by hand or with a power tool until the tool shoulder bottoms out on the case bottom.
The measurements given in the table above are the diameter of a circle that held all of the shots. The groups did not contain any obvious flyers.
During my initial trip to the range, I fired group “A” and “B”. I was confused by the results of group “B” and so I went back a second time and shot group “C,” which better matched my expectations.
My conclusion from this testing is that I will deburr and neck size all of my reloads for these rifles since they appear to increase the accuracy by 31 to 35%. Neck sizing alone was beneficial, but I would not have seen a significant improvement without also deburring the flash hole. This testing also gives me some hint of the benefits of using a better brand of brass instead of the least expensive brand.
I have two final observations on neck sizing as compared to full sizing. The first is that both methods resulted in cases that fed correctly in my bolt action rifle. The second observation is that neck sizing saves time since I do not have to lubricate the case exterior and neck interior prior to the sizing operation.
Copyright 2010 by Andrew Willis. All rights reserved.