Thursday, November 1, 2007

Reloading accurate rifle ammo: Neck vs full length sizing

Hand loaders have so many choices, so many things to keep them up at night, I thought I’d add some fuel to the fire.

Let’s look at yet another factor in loading accurate rifle ammunition, the method chosen to size the case.

Usually one of two avenues is open to us; Full length sizing and neck sizing.

Full length sizing is just what it sounds like: The case is ‘resized’ along its entire length. The die can be adjusted to change the depth of this sizing, or how far down the neck and body the case is pushed into the die body.

Neck sizing involves just working on the case neck, leaving the body as fired. This alternative has several side roads of its own.

Why is one type of sizing preferable to the other? Here opinions abound, but lets look at a few of the major points.

Full length sizing assures the case will meet specification, and fit in almost any chamber of that caliber that also meets specification. This means ammunition feed and function should be reasonably trouble free. A shooter using his rifle for hunting, some competitions, and defensive uses must consider this factor of utmost importance. In addition, many semi-auto rifles do not function well with cases right at chamber size.

Neck sizing has the advantage of leaving the fired case expanded to match the chamber of the rifle it was fired in. This closer fit promotes accuracy, pure and simple. Neck sizing also works the case less, promoting brass life. As icing on the cake and unlike full length sized cases, neck sizing requires minimal lube. That means one less mess to clean up. Even with these advantages, cases fired with full power loads often must be full length sized every third or fourth loading to preserve function. Bolt action and single shot rifles are best suited to take advantage of neck sized cases.

There are several types of full length sizing. Most commonly encountered are standard sizing and small base sizing. Small base dies take the base of cartridge back down to minimum dimensions, and are usually reserved for ammunition used in semi auto rifles with tight chambers. These creatures can be found at national match ranges, with highly experienced shooters hovering over them like a momma bear with a cub.

Neck sizing boils down to two basic types as well: standard and collet sizing. Standard neck sizers squeeze the case neck into proper dimension, while leaving the case body as fired. They first smoosh the neck into a tight hole that makes it smaller, then drags it back over an inside neck sizer that opens it back up to final dimension.

Collet neck sizing inserts a final dimension form into the neck then uses a collet to squeeze the neck onto the mandrel. The brass is worked only once, and it’s not pushed around at all.

In order to better understand and picture the differences between full length and neck sizing, lets look at a pair of cases done one in each method.

For our purposes I chose a LEE die set containing both types of die in 8x57mm.

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The collet neck sizing die, once disassembled, reveals the mandrel and neck collet along with the tapered sleeve that squeezes it around the case neck.

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A standard neck sizing die, and even a full length die, is quite easy to set up and use. It’s fairly intuitive and the results can be seen and felt as soon as the case is inserted and removed. The collet type die is more complicated, and the builders directions should be followed closely. A mistake here can snap the collet and destroy the die. Trust me on this..... I know this to be true.... sigh.

The standard sizing die is much simpler in design. The body of the die is very closely machined to final case dimension, and the de-capping stem contains an inside sizing button that expands the case neck to final dimension as the case is removed from the die.

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In full length sizing, the case must be lubed over it’s entire outside, and a bit of lube on it’s inside neck as well. I use a lube pad when doing just a few cases, and a spray lube when doing a larger batch.

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When neck sizing, full lubing is not required. Only a tiny bit of lube on the inside and outside of the neck is sufficient. For this, I push the case mouth against the lube pad and give it a slight twist. That’s all the lube needed!

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I struggled finding a way to visually demonstrate the actual results of sizing. Holding the cases in hand, the end product is obvious. Trying to make it clear in photographs was a different matter completely.

I hit upon the idea of ‘smoking’ the cases. This involves an open flame from a match or a candle played across the object, leaving a very thin coat of black carbon behind.

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Smoking the fully lubed case proved to be an obnoxious task, as the oil simply did not wish to take on the carbon. The dry case application was a snap. This is an old time way of marking up a part for fitting, and leaves a contact map easily viewed, and measured if need be.

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Running each case properly into its particular die according to the manufacturers directions, we are left with two cases marked up to clearly show the difference between full length and neck sizing.

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The difference in the neck treatment is clear. The full length die forces the case neck into a hardened steel hole, while the collet die squeezes the neck against a mandrel with out over working the brass.

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The kind of sizing chosen by the hand loader is just that..... a choice. Most folks are quite happy to stick with full length sizing, or ‘mostly’ full length sizing accomplished by backing off the die a bit. Experienced loaders searching for maximum accuracy often rely on neck sizing as one step of their process.

People loading one caliber for several rifles must either full length size or dedicate one batch of cases to each rifle, if neck sizing for accuracy is the method used., Neck sized cases don’t usually work well unless used in the same rifle each time.

Consider it just another tool in the *large* tool box available to hand loaders.

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