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Converting Brass

By Matthew Cameron

Sourcing brass cases is not always a matter of dropping into to your local gun shop, for several years now we have suffered a shortage. Here in Australia and New Zealand we're lucky to have ADI producing .223, .308 and .243 Win brass of high quality.

 

But for other calibres you may not be so fortunate. You may have to shop around, and premium brass comes with a cost to match.

 

As I've mentioned before I came across a simple method for solving problems - the ABC method:

  • Assume Nothing
  • Believe Nothing
  • Check Everything

 

Nowhere is the above more applicable than in the forming or converting of cartridge cases from one calibre to another. There are a couple of factors that stand out.

 

There are cases that require minimum changes to convert them to another calibre with a minimum of tools, perhaps nothing more than new sizing and decapping dies, but other cases such as the Ackley Improved line require fire-forming to the new configuration. The third type requires extensive working to arrive at the finished product and may require some extra tools.

 

“...factory rifles are generous in the dimensions between the walls of the neck and the chamber. Reducing this is a known accuracy enhancement, simply because the centreline of the case is more in alignment with the centreline of the bore.”

 

Forming any of these cases requires a great deal of research followed by adequate lubrication and annealing. Due to the forces involved adequate lubrication is paramount. In forming cases I have only ever used STP oil treatment and Imperial Sizing Wax, both have proven to be a success. There are probably other suitable products but I haven't tried them.

 

Imperial Sizing Die Wax is one of the best lubricants available for case forming.

 

One of the best ways to prolong brass life is by annealing. There is a lot of noise on the internet about the process. For the reloader it can be done cheaply and efficiently with a minimum of tools. My preference is to anneal the cases once the final forming is complete in addition to any other annealing during the process.

 

I use a chef's cooking torch picked up off the internet, it cost around $30.00. Its only requirement is that it should produce a pencil flame. It's powered by butane gas and we buy the cylinders at our local automotive store.

 

The only other tool required is something to hold the case, you can use and electric drill or screwdriver together with a shell holder or a claw pickup tool (hardware or automotive). The claws conveniently fit over the heads of most cartridge cases.

 

To begin annealing place the base in the pickup tool and direct the tip of the flame at the junction of the case mouth and the neck down towards the shoulder, then rotate the case slowly in the flame.

 

After about 5 seconds just down from the shoulder the brass will turn brown, then rapidly turn to a bright blue. Proceed over the junction of the shoulder onto the body of the case just a little.

 

Properly annealed cases, note the blue ring on the shoulder.

 

When the colour has reached approximately 1mm down the case body remove the flame and drop the case into a pot of water. It takes 9 to 10 seconds for the whole process. Some pros will tell you that quenching is not required, but I do it anyway.

 

Personally I gave up fiddling with temperature liquids (you paint the case with them and they change colour as temperatures rise) - all I can say is that the above method produces cases annealed to the right temperature and split necks are now almost unknown on our reloading bench.

 

Commercial cases are all annealed at the factory but the temperature marks are polished off before final packing.

 

NOTE: It is VITAL that only the necks and shoulders be heated. The main body of any case should not be softened by heat - it has to be hard enough to contain the pressure of the rapidly expanding gas when the cartridge is fired.

 

Two methods of holding case for annealing. The claw holder type can be purchased from hardware stores.

 

Annealed necks also produce consistent “grip” on a projectile, a known accuracy enhancer. If youre using straight line dies you can control the amount of “grip” with different sized bushings. It is normal to use a bushing .003 inches less than the projectile.

 

I've found that there is some variation between cases but there are small tools available that accurately measure the size of individual case mouths. If you are processing different types of cases the only other useful tools are a tubing micrometre (for case neck thickness) or a caliper which you probably have anyway.

 

FIRE-FORMING

Let’s start at the beginning. The easiest cases to form are the Ackley Improved. In simple terms you fire the parent case in the Ackley chamber and end up with a case that is slightly “blown out” at the shoulder, thus giving it a modest increase in powder capacity and hence velocity. Usually the shoulder of the case becomes steeper; this prevents potential brass flow, hence less trimming.

 

As an example the parent .308 case was also used as a basis for the .243 Winchester. We make all our .243 Ackley Improved cases out of either ADI .308 Winchester or ADI .243 Winchester brass.

 

As expected due to the extra stepping down the .308 Winchester has a thicker neck than the .243 brass and is fractionally longer, it averaged 0.016 to 0.017 inches in thickness and 2.225 inches in length.

 

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In contrast the ADI .243 brass averaged 0.014 to 0.015 inches in neck thickness and a neat two inches, just 0.045” below the parent case maximum. Both cases produced sub-MOA accuracy in the Ackley barrel.

 

Note that the .308 cases were annealed after necking down in our 7mm-08 “form and trim” die and again after final forming. Some of these cases have already passed through the loading and firing process six or seven times, case loss zero and no split necks.

 

“At this stage I should mention a couple of items that need to be checked continually as you proceed: case length and neck thickness, both will alter during the process of changing one case to another, remember the “C” in the ABC above.”

 

Both types of cases were fire-formed in the Ackley barrel using 15 grains of W-296 powder topped up with Polenta from the supermarket and kept in place with a small wad of toilet tissue.

 

The fire-forming did produce cases with a rounder shoulder but these became much sharper when loaded with a full powder charge and a projectile; the low-charge method was used to protect barrel life.

 

MINOR CHANGES

The next types of cases are those that require only a slight change in dimensions. Typically the parent case is a .30-06 with the finished product being either a .270 Winchester or a .25-06 Remington. You can proceed in one of two ways.

 

Either lubricate a .30-06 case well, then simply run it through a .270 or .25-06 sizing and decapping die - or if you prefer straight into a form and trim die of the appropriate calibre.

 

Where the change in diameter is not large either technique will work. We have manufactured cases in these calibres from virgin .30-06 brass without any problems, just ensure that you don't get the various head stamps mixed up!

 

Form and trim dies are available in most calibres and are a must when converting brass from one calibre to another.

 

Another case in this class is the .257 Roberts; the brass can be formed from 7x57mm Mauser or with extra work involved, a .30-06 case. Using a .30-06 case a form and trim die would almost be a requirement as the case will have to be cut to length, it should also be annealed several times.

 

I recently cancelled a .257 Roberts project; several issues forced this decision, the lack of brass and the difficulty in attaining suitable forming dies contributed. The lack of brass in this calibre also exists in the USA; in addition it is not a very popular round in either Australia or New Zealand.

  

The idea was straight forward enough, by using the improved cases and a longer loaded length overall, it would have been possible to increase the powder charge up to ten grains, perhaps adding 200 to 250fps in velocity.

 

One of the advantages of using straight line dies is that neck diameter can be controlled via bushings, an important factor when you're converting cases.

 

Form and trim dies are my preferred method of keeping cases trimmed to length, unlike body dies they do keep the necks to size.

 

You cannot make a mistake, just ensure that the base of the die is in contact with the shell holder, insert the lubricated case and file off any metal that is above the die, chamfer inside and out, job done. I have never found them as a stock item in any Australian gun shop, hence ours are all imported.

 

At this stage I should mention a couple of items that need to be checked continually as you proceed: case length and neck thickness, both will alter during the process of changing one case to another, remember the “C” in the ABC above.

 

Length can be checked in an appropriate form and trim die or with a normal caliper. Neck thickening might be a problem at a later stage depending on calibre and the degree of necking-down.

 

When converting cases, it's important to check the final length with a good set of calipers.

 

Secondly, depending on which case you are necking down or changing the shape of, be aware that even with good lubrication a lot of force is required, hence we have to address the strength of the press. I have only ever owned an RCBS Big Max which was purchased more than thirty years ago after some sound advice.

 

The next case in this class may cause problems depending on the individual rifle, simply because the round, the now ancient .303-25 always was a wildcat, hence variations exist in relation to case length depending on the whim of the individual gunsmith.

 

“The easiest cases to form are the Ackley Improved. In simple terms you fire the parent case in the Ackley chamber and end up with a case that is slightly “blown out” at the shoulder, thus giving it a modest increase in powder capacity and hence velocity.”

 

After researching my library the case length varied from a low of 2.185 inches to a high of 2.222 inches, of course the cut of the chamber would be the final controller in an individual rifle.

 

Oddly enough we had just finished loading 100 rounds for a friend’s rifle; we had loaded for this particular rifle as far back as the early 1980s. The Bertram cases were trimmed slightly to an average 2.206 inches in length to fit freely into the chamber.

 

Although we had formed .303-25 brass from straight .303 cases previously, a quick look on the internet showed that both empty brass and loaded ammunition are available. You have to balance time and effort against cost when converting or attempting to convert cases to another calibre.

 

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One of the very early conversions, .303/25 from the parent .303 case.

  

The other parent case that would fit this “one run through the new die” situation is the .308 Winchester which has numerous offspring.

 

The first to consider is the 7mm-08. We have formed such cases again by simply lubricating the case and carefully inserting it in either a 7mm-08 form and trim die or a straight 7mm-08 decapping and sizing die, or sometimes a combination of the two to ensure correct dimensions, this was a straightforward exercise.

 

THE .22-250

Another case that can be formed from .308 or .243 brass is the .22-250 Remington; it does however pose some problems. Our cases were necked down in three stages with annealing after each step, they were .308 Winchester case into 7mm-08 form and trim die, then a .243 Winchester form and trim die and finally a .22-250 Remington form and trim die.

 

The excessive length was trimmed with a fine hacksaw blade and the mouth chamfered inside and out, the brass thickness measured was excessive, however there are some circumstances when this could be used to advantage.

 

Average normal thickness of .22-250 Remington American brass at the case mouth is 0.013.inches. An ADI .243 case was reduced to 22-250 Remington size by running a heavily lubricated case in a .22-250 Remington form and trim die.

 

A standard .22/250 case (left) and an ex-.308 case on the right converted to .22/250 Remington via a .243 Winchester form and trim die, note the rounded shoulder and larger extractor groove.

 

It was of course over length. The excess was removed with a fine bladed hacksaw, the mouth filed flat and then chamfered inside and out, the thickness of the neck had increased by a nominal 0.001.

 

Note that the shoulder of the case is rounded, but this will expand on the first firing. If we had used an ADI .308 case and reduced it in three steps to .22-250 Remington the case mouth would have increased further in size which may have created an excessively thick neck.

 

“The easiest cases to form are the Ackley Improved. In simple terms you fire the parent case in the Ackley chamber and end up with a case that is slightly “blown out” at the shoulder, thus giving it a modest increase in powder capacity and hence velocity.”

 

It is a known fact that factory rifles are generous in the dimensions between the walls of the neck and the chamber. Reducing this is a known accuracy enhancement, simply because the centreline of the case is more in alignment with the centreline of the bore.

 

In addition if the case neck thickness will not fit in an individual rifle’s chamber it may be trimmed to the desired figure via neck turning.

 

The other calibre I have investigated is the .257 Weatherby Magnum. It's parent is the .300H&H but cases may be made from 7mm Weatherby Magnum brass - this will leave the cases somewhat short but still useable. With use however there should be some case lengthening.

 

An ex-7mm Remington Magnum case (left) after a single run through the .257 Weatherby Magnum form and trim die, standard .257 Weatherby case on right.

 

So far we have been able to find sufficient cases and have not had to manufacture them out of 7mm Rem Mag brass. However we ran a lubricated 7mm Rem Mag case into the .257 Weatherby Magnum trim die, and while it easily reduced the neck diameter not much of the Weatherby double radius shoulder was evident, the case would have to be fire-formed with 20gr of fast powder and Polenta filling.

 

Note that at this stage before fire-forming the case with a reduced neck would fit in the rifle’s chamber.

 

OVER THE COUNTER CASES

Kiwi shooters should remember that the Bertram Bullet Co manufactures cases in many “normal” and obscure calibres in Australia. It is highly likely that they have a parent case suitable to be modified or perhaps exactly the case you need, so do your research once again.

 

For those of you who want to convert cases of any sort I suggest a couple of useful items. Firstly there are two publications: “Designing & Forming Custom Cartridges” by Ken Howell (1995), secondly “The Handloaders Manual of Cartridge Conversions” by John Donnelly (1987). ABC applies to both but they contain a wealth of information, both appear on the internet for sale.

 

Finally, converting cases to another calibre may be a time consuming process, don’t forget to purchase a stuck case removal kit from any of the major makers of reloading equipment - it is likely you will use it more than you think!

 

Shoot safe,

 

Matthew

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