Full Length, Partial & Neck Resizing the 303 British

Copyright 1999 – Stephen Redgwell

Shooters always debate about which method is best for reloading rimmed cases like the 303 British. The argument will never be settled, but here’s what I do.


Assuming that you don’t grossly overcharge the case, any serviceable action will easily contain the pressure generated on firing. At that instant, building pressure pushes on the brass – equally, and in all directions – looking for a place to vent. The case acts as a seal and closes off all escape routes for the gas, by pressing against, and conforming to, the sides of the chamber.

The seated bullet is the weak link. The pressure acts on the base of the bullet and begins pushing it down the barrel. This is the way all metallic cartridges are designed to work.

But what happens inside the action if the case is damaged?


Trouble starts when pressure builds to a point where the case can no longer contain it. The pressure must vent, but where does it go? It acts on any weak areas – forcing through cracks or thin spots. Burning powder, flame and other debris also travel through these spots as well. The size of the cracks and the action design will determine how much damage will be caused by all of this. So how do these cracks and thin spots develop?

Thin spots develop forward of the rim
Cracks usually appear on the neck or shoulder


The two most common problems are case neck splits and case head separations. Theses splits, cracks or thin spots on the interior of the case wall reduce or completely thwart the case’s ability to contain any pressure on firing.

Case Neck Splits

The most common cause of case neck splits is called work hardening. This is brass that has been continually resized and fired. Over time, the constant stretching and compression of the neck cause it to become brittle, ruining its elasticity. Like leftover turkey skin after Christmas, it cracks rather than stretches.

You have two options to slow down the progress of splits. The first is to anneal (heat treat) the case necks. The second is to use a Lee Collet Die.

Case Head Separations

At the other end of the case, there can be a problem with separations. They are caused by a combination of events which leads to total case perforation near the head – this is the area just forward of the rim. (Fig. A – below) The perforation starts as a gradual thinning of the case wall. The thinning is caused by brass flowing forward from the head area upon firing. This creates a thin spot at the case head. (Fig. B – below)

Any case with a small shoulder angle, that is fired using maximum loads, will have brass flow. It moves toward the case mouth at a much greater rate than cases with more steeply angled shoulders. Improved or Ackley type cases with 35 or 40 degree shoulders are examples of brass with steep shoulders.

When you fire and full length resize your cases over and over, this aggravates the situation. Brass will continue to move forward. The weaker spots on the case are flexed, squeezed and contorted. Case necks become brittle.


Case Design. Cases whose walls are thin to begin with are more susceptible to failure. Examples include the 22 Hornet, 30/30 Winchester and the 303 British.

Case Material. Cases made from materials other than brass, or brass manufactured to different specifications other than the standard 70/30 copper-zinc mix.

Mercuric Primers. Previously fired brass that was primed using mercuric primers. The mercury fulminate mixture in these older primers adheres to the brass when fired and weakens its structure. It also causes brittleness.

Avoid the use of older cases whose history is unknown. Avoid the use of cases whose headstamp is unfamiliar to you, unless you can reasonably confirm its loading composition.

Despite the use of lead styphnate in most primers since the mid 30s, mercuric primers were still manufactured and used as late as the 1960s. It’s possible then, that ammunition containing these primers may still be available. Really low cost ammunition is a good sign that what you are getting is corrosive and/or mercuric. Beware!

Lee Enfield Chambers. Some chambers are cut so long that any case must “stretch a mile” to conform to it. A maximum stretch means a maximum compaction with full length dies.


Full length resizing forces the case back to its approximate original size. It squeezes the sides of the neck, case wall and pushes the shoulder back. As mentioned earlier, this really compacts and contorts the case, which accelerates splits and cracks. This should only be done when the shoulder moves too far forward to allow proper cartridge chambering. A better idea would be use of a Redding body die. It only moves the case walls and can be seated in your press to move the shoulder back only as much as will allow uninhibited chambering.


Many people mistakenly believe that this is the same as neck resizing. It’s not. Adjusting a full length sizing die by backing it out a thread or two, may not push the shoulder back, but it partially squeezes the case wall. This can cause the neck to shoulder length to increase – sometimes making the brass too long to chamber properly.

If adjusted to move the shoulder back slightly, still more of the case wall is squeezed. Any needless body resizing overworks the brass and it’s not needed. It shortens case life.

Since most 303 chambers are cut large, partially resized cases still expand to the maximum when fired and then compress when resized. You end up with almost the same result as when full length resizing.


This reduces only the diameter of the neck, leaving everything else untouched. This works the brass the least and is the best way to extend the life of your case. You will save some time and lessen the strain on yourself and your equipment.

Here’s a cheap trick – buy or borrow a Lee Loader. Its simple design will let you easily and inexpensively explore the world of neck resizing with your rifle. You will be surprised with the performance of what many consider to be a slow and poorly made die that produces “substandard” ammunition. Believe it or not, it’s faster than you think. No lube is required, so preparation and clean up are virtually non existent. Just wipe the case neck before you resize.


“Make sure you full length/partial resize if you’re going hunting! Don’t ever neck size!”

Hearing stuff like this makes me chuckle. Reloaders use a lot of different excuses as to why they won’t neck size. Some worry that dirt or water could build up in the chamber. Others want to ensure the cartridge enters without resistance.

Check all your cartridges before you go!! All cartridges should be checked prior to the trip for proper functioning. Load each one into the magazine and feed them into the chamber when you’re at the range. This will eliminate any potential case problems before you go.

Debris in the action. Some people that partially resize say they want to push back enough of the case wall to ensure 100 percent feeding – in case dirt or other debris finds its way into the chamber.

Reloaders that resize enough of the case so that it is “headspacing off the shoulder” have left no room at all up front! There goes most of their theory about allowing for build up!

Make sure you clean your chamber daily when hunting – even if you don’t fire it.

Use an action cover. Commonwealth armies used them and so do many black powder hunters. A piece of cloth or canvas is a lot less headache than repeatedly going through a full length sizing routine.

Cartridge Debris. Keeping cartridges clean and protected from the elements is smart. Keep them in a covered ammunition pouch along with your neck sized cartridges, never loose in your pocket!

Psychological Debris. Finally, if you absolutely believe that fully resized cases are important to have, keep a couple loaded with the same recipe, but neck size the rest. Mark them by covering the entire base with a solid colour – blue or red – using a permanent marker for instant identification.


1. As proven by benchrest shooters, neck resizing provides the longest lasting cases.
2. Neck sizing is easier and quicker to perform because case preparation and clean up are less.
3. Less physical force is needed when only resizing the neck. That’s easier on you, your equipment and the case.
4. Accuracy is almost always better because the case is custom fit to the chamber.
5. More reloads means more money saved, less time at the bench and more time shooting!