Fireforming. "You only get one chance to make good brass."
Updated: Apr 30
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.
Note: I am a short range Benchrest competitor and hunter. I typically make 50 cases per barrel. The following process has worked great for me. However, if you are a high volume shooter, you may want to research other methods that do not use bullets to fireform the brass.
Most virgin brass was annealed at the factory. Annealing does not need to be done if the only process is to bump the shoulder back. I anneal before fireforming only if the necks have to be expanded (necked up) or reduced (necked down).
2. Check Length
The brass that I have experience with all pulled back (shrunk) when fireforming. This is not to say that all brass shrinks, just I have never experienced anything else. Due to that experience, I like to have all brass slightly (.002-.005") under max case length.
3. Chamfer and Deburr Necks
Chamferring and Deburring needs to happen regardless if the brass is trimmed or not. This will allow for smooth bullet seating.
Experience Tip: Do not load up all the cases you want to fireform until you know the correct chamber measurements. Follow steps 4-9 with ONE piece of brass. From this newly formed piece, apply the correct measurements for the remaining pieces. It is not unusual for the first piece to be a "sacrificial lamb".
Take accurate notes while fireforming. (shoulder bump, neck bushing, seating depth, powder charge, etc) There is a good chance adjustments will need to be made.
4. Bump the Shoulder.
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.
When brass is being fireformed for an Ackley chamber (40 degree shoulder) the case should have a slight (.002 - .004") crush fit. This is the optimal situation and not always possible due to the variability of the virgin brass.
A very good question is: How do I know where to put the shoulder if I do not have any measurements to go by? The answer is; You don't know. Hence the reason for only fireforming one piece of brass to start with. From that case, accurate measurements can then be taken and applied to the rest of the cases.
5. 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.
6. 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 in the upper 34 grains of H4198. When fireforming 30BR brass, I will use a charge around 33.5 gr of H4198.
For "new to you" cartridges, refer to a loading manual for powders and charges then subtract 1.5 grains. Remember to keep accurate notes in case changes need to be made for the remaining cases.
1. This picture shows the result of not enough pressure to "snap" the shoulder. When rounded shoulders like this appear, adjust type of powder or amount of powder.
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7. 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.
Experience Tip: Picking the correct powder can also help in this area. A powder that is at or near 100% capacity makes it harder for the bullet to be pushed back into the case helping to push the case head against the bolt face.
8. Lightly Oil the Case
Spray your favorite gun oil on a rag. Lightly, roll the case body and shoulder through the oil before chambering the round. Just the thinnest layer of oil will keep the brass from sticking to the chamber walls and allow the case to “flow” during expansion.
Fire the loaded cartridge in the desired chamber. Check for pressure signs while fireforming. You may need to adjust the charge on the remaining pieces,
From this piece of brass, accurate measurements can be taken for shoulder bump, COL, as well as any adjustments needed to powder charge. Being mindful of these adjustments will ensure the rest of the pieces will be fireformed correctly.
When it comes time to fireform multiple pieces of brass, many competitors will use this time to rough sight-in their scopes and to practice reading conditions. Very little emphasis should be placed on how the rifle groups while fireforming brass.
Left: Virgin 6 BR brass expanded to 30 cal
L2: Once fired 30 BR
L3: Virgin 6 mm Rem
Right: Once fired 6 mm Rem Ackley
After fireforming all pieces, I will anneal to relieve the stress induced into the brass during expansion to the new dimensions. This annealing will allow the cases to fully shape on the following firings.
It usually takes three firings to fully shape the shoulder and to get a true mimic of the chamber. This is why many custom die makers want to have three firings on the case before you send it to them. 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 third 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 (Ackley is .003 crush fit). 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.
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.