Sierra Bullets

Written by Sierra Bullets Ballistic Technician Duane Siercks

What is fireforming?

Fireforming is the process of creating custom fitting cartridge cases for your specific firearm. Having the “custom” cases can be very beneficial and really isn’t to hard to accomplish. I want to hopefully shed some light on the process as we continue. When we buy shoes and clothes, we like for them to fit “just so”. We all have our own opinion as to what “just so” feels like. Each firearm has a preference for certain things in a load that is being used in that firearm. It may be bullet weight or style; it could certainly be a powder selection and amount. These are just a couple of examples to be found on a rather long list of items that need to be considered during the reloading process.

Fireforming is also one of those items. This involves the controlled forming of the case and also the very controlled re-sizing of the fireformed case. There is also another use for fireforming, and that is called case-forming. This is actually taking one cartridge and alter the case to form another cartridge. Such cartridges as the Ackley’s or Improved come to mind. Then also you have the many varied wildcat cartridges. This process often requires fireforming to be done. But rather than allowing this to get too far from the intended subject, I will to stick to the fireforming subject.

Why do we want to fireform?

Fireforming has two major goals.

1. Extended case life.

Brass case demand is very high right now, and supply is a bit short. So, of course, this causes brass prices to be very high, if and when you can find what you need. Fireforming can be a big help during this situation by helping to insure that your cases last as long as possible. If done properly, you can be guaranteed that case life will by extended by quite a bit. This does not excuse us from careful observation of case and load issues that can and do arise. It does certainly minimize case stretching and case loss due to excessive and repeated stretching.

2. Potential for better accuracy

Note that in the semi-autos (that are extremely popular) and lever action firearms that full length sizing is very much recommended. Due to their inability to chamber cases that are not full length re-sized is very limited.  A custom fitted case can give you a much better opportunity at accuracy due to eliminating some accuracy robbing issues. When you are full length re-sizing, you almost always create problems that can certainly rob you of accuracy performance A fireformed case helps to align the bullet with the center of the bore which is always beneficial when trying to squeeze out the last smidgen of accuracy.

How do you fireform ?

I want to mention that there is certainly more than one way to fireform. I will endeavor to help you understand the concept and explain the more common version of fireforming. I will also mention some other variations that are used too.

The most common way:

With a new case, we will want to seat a primer first off. The next step requires us to determine at what length the bullet (we want to use in the fireforming load) will touch the rifling. (It is best to use a heavier weight bullet for the cartridge and if available a flat base bullet.) Then, select a powder for the cartridge you are working with. The better powders are those that fall in the middle of the burn rate range for the cartridge and bullet weight. Use a mid-range load with the powder and bullet selected. Then seat the bullet to touch the rifling. The bullet touching the rifling causes the cartridge rim to be in contact with the bolt face or receiver, so that the firing pin strike cannot cause the case to be shoved forward. This then allows the case to expand to the chamber dimensions with out the weakening stretch that otherwise would take place. It is always best to use new unfired cases. Cases that have been previously fired, whether it be factory ammo or cases that were loaded and not fireformed first, will almost always have a certain amount of stretch that has occurred. This initial stretching is usually when the most damage occurs.

Sometimes the throat in a particular chamber may be long enough that seating a bullet out to touch the rifling may not be possible. In that situation, hope is not lost, we have other ways of dealing with the scenario. In this situation, we will need to run the neck of the case across a larger expander button. This can be done by getting a larger caliber tapered expander button from the die manufacturer. Some of the die manufacturers offer complete decapping rod assemblies with the tapered expander buttons. Going with one of those a couple of calibers larger will work very well. There are also expander dies made and sold that have interchangeable mandrels that would facilitate this process.also. Making sure to sufficiently lube the inside of the case neck, run just the neck portion over the expander button. This will cause the neck to expand to the larger diameter. We then will want to put the original expander button back on and adjust the die so that we are sizing a small portion of the neck back down to original diameter. We are not sizing the full length of the neck. We want to leave enough of the neck expanded so that it will help hold the case firmly against the bolt face, minimizing the case damaging stretch. But we also need a small portion of the neck holding the bullet too. This requires careful adjustment of the sizing die to get neck expansion/resizing amount just right.

Another scenario for fireforming is the simple necking up or down of an existing cartridge to create another case/cartridge. The following are the steps that I use to create 6.5-06 cases from 270 Win. cases.

1. I first start off with new 270 cases. The chamber of my 6.5-06 will not accept the full length 270 case which measures 2.540″ in length. I will trim the cases back to a length of 2.497″.  I then chamfer and de-burr.

2. The next step will be to adjust the 6.5-06 sizing die to partially size part of  the length of the case neck. This may require some fine adjustment. You will want to size only a small portion of the neck and then try chambering in your firearm to see if the bolt will close. Do not force the bolt closed. Then keep adjusting the sizing die farther down slowly and trying them in the chamber until you get the bolt to close. This is important, as you want the un-sized portion of the neck to help hold the case back against the bolt face in order to correctly fireform. Once this sizing was done, I checked the length again to be certain that the case would still fit in the chamber. The length had grown to 2.500″ and still was chambering very well. Perfect.

3. Now we are ready to fireform. Pick an appropriate burn rate of powder for the cartridge. Starting just slightly under the mid-point of the powder charge range for the bullet weight you will be using. Load 2 or 3 and fire them in the rifle. If the cases look like the shoulder is formed, and the neck looks filled out, then the charge is sufficient. If not, then increase the powder charge about one-half grain until the case is formed.

4. At this time we are ready to re-size the case. Care must be taken when re-sizing that we do not undo the fireforming. We want to size as much of the case neck as we actually can and still not move the shoulder back any at all I do this by adjusting the sizing down very slowly and watching how far down on the neck it is actually sizing. You can visually see the progression. Go slow and make  small adjustments to reach your goal. You are now ready to start your load development with fire-formed cases.