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Fireforming. "You only get one chance to make good brass."

Updated: 5 days ago



Fireforming brass is the process of expanding a virgin case to match the chamber dimensions. This process is done every time the cartridge is fired. However, the term fireforming commonly applies to the very first firing of new brass.

Fireforming is a non-issue if you are a shooter who buys their ammo over the counter. If you reload your own ammunition, this is a pretty big deal. The goal is to expand the brass to the same dimensions as the chamber. Handloaders then purchase the correct sizing die so the proper amount of resizing takes place. There are many benefits to this such as: extended case life, decreased work hardening, and increased precision/accuracy.

During fireforming, the brass will (theoretically) expand to the chamber then naturally contract, allowing the brass to be ejected. In reality, this does not always happen. There are a few key points that need to be addressed to ensure that it does.


Experience Tip: Do not load up all the cases you want to fireform until you know the correct chamber measurements. Load and fireform ONE piece of brass. From this newly formed piece, take all the needed measurements for the remaining pieces.

Bump the Shoulder Back.

The case shoulder should be bumped back roughly .005-.010” from the actual chamber dimension for the first firing. This will allow the shoulder to get “some momentum” which will help shape the shoulder. Many times, this setback is already there when using new brass. If not, simply adjust the resizing die for the correct amount of bump.


Use Plenty of Neck Tension.

I prefer to use a bushing that is .004” smaller than the over bullet measurement when fireforming. More on why this is important later.


Use a Stout Load.

I use roughly a grain and a half under what I think the final load is going to be. For example; the final load in my 30BR is usually around 34.8 gr of H4198. When fireforming, I will use a charge around 33.5 gr of H4198.

Experience Tip: Check for pressure signs while fireforming. You may need to adjust the charge, depending on how much you are moving the case. Yet another reason to only load and fireform one case to begin with.

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Seat the Bullet Long

I routinely use a seating depth of +.025” (jam) or more when fireforming. A prerequisite in meeting the end goal is to start with the base of the case tight against the bolt face. Seating the bullet long and using plenty of neck tension work together to help meet this requirement in two ways. First, when the round is chambered, this combination will ensure the case is pushed backward tight against the bolt face. High neck tension and long seating will also keep the case from traveling forward when the firing pin strikes the primer. Both of these are key points in the fireforming procedure.

Lightly Oil the Case

Spray your favorite gun oil on a rag. Lightly, roll the case body and shoulder through that oil before chambering the round. Just the slightest layer of oil will keep the brass from sticking to the chamber walls and allow the case to “flow” during expansion.


Anneal

Most virgin brass was annealed at the factory. If the only process was to bump the shoulder back, you should be good to go for the first firing. I only anneal before fireforming if the necks have to be expanded or reduced.

After the fireforming, I will anneal to relieve the stress induced into the brass during expansion to the new dimensions. This annealing will allow the case to fully shape on the following firings.


3 Firings

It usually takes three firings to fully shape the shoulder and to get a true mimic of the chamber. However, the brass is formed enough after the first firing that the handloader can start the tuning process.

Fireformed brass will need to be trimmed to uniform the case lengths. I like to trim the brass after the second firing. Case lengths will then be periodically checked for uniformity.

As stated earlier; I use .005” to .010” of shoulder bump for the first firing. On succeeding firings, I will only move the shoulder .0005 - .001” on competition brass and .001-.002” on hunting brass. To achieve these measurements, it is not unusual to adjust the sizing die, each time, up to the third firing. Subsequently, the shoulder dimension should be fully formed and case work hardening is usually the determining factor if the die needs to be adjusted.





Left: Virgin 6 BR brass

Middle: Once fired 30 BR

Left: Completely formed 30 BR







Credit needs to be given to Al Nyhus (SD), Randy Robinett (IA) and Mike Bigelow (IA) for sharing their proven case forming techniques. I simply combined what I liked, from all three, to make this procedure.

In much the same way, that is what Connect The Dots is all about. Taking bits and pieces of proven information and combining it with what you already do. This will make your current procedures better, which will carry over in the form of increased accuracy and precision. Until next time, enjoy the experience.





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