Reloading 101: Fireforming Cases

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.


middle-step2. 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.

img_69734. 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.

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37 Responses to Reloading 101: Fireforming Cases

  1. Pingback: Reloading 101: Fireforming Cases — Sierra Bullets |

  2. firstriverbend says:

    Much better description of how to fire form a case than any others I have read!
    Some articles I have read, several actually, stated to just place a few grains of fast powder like Bullseye under a wad of kapok or cotton filler material. Those came with the disclaimer of “some case may split”, no kidding!!
    While I have learned to reform cases over the years, one thing I have found is much of the information out there is poor at best, dangerous too often. This article on the other hand goes to what I have learned; take your time, be precise and think through each step! You will have excellent cases when you are done, along with extremely few failures, either in the initial production or during later reloadings of your “new” cases! 🙂

    Thanks for an excellent article!

    Liked by 1 person

  3. Ron says:

    Just starting to shoot a 6.5 Creedmoor and will be reloading the empties. Would this process work on previously fired brass as well as new brass? I’m thinking it probably would. That said I do have some new brass also.


    • Yes Ron, but we usually only do this with new brass. The once fired or previously fired case will have already been stretched upon the first firing unless we do the correct fire-forming. You might still enhance accuracy though. – Duane Siercks, Ballistic Technician

      Liked by 1 person

    • firstriverbend says:

      I really agree with Duane’s comment about preferring to use new brass! The main reason to me is the expense and time. Using once fired can appear cheaper on the front end, but in the long run it is always more expensive. The reason is quite simple, fire forming take a lot of time and the expense of a bullet, powder and primer all adds up. Doing it the correct way takes just as long and is as expensive with used brass, but you will not have as precise of a finished product and it will certainly not last as long in use as the new brass is going to. A piece of new brass can be formed to be exact, without the stretching you are going to encounter with used brass, even if you cannot see the stretching, it will be there and it will help to shorten the life of the brass. If you do not care about the life, then it does not matter, but once you have a piece of brass you made yourself fail prematurely, my bet is disappointment. Personally I have used cases in excess of 40 loadings, when they would finally fail, it was like losing an old friend. 😦


  4. Bart Bobbitt says:

    What centers the case neck, and therefore the bullet, in the bore when a rimless bottleneck case headspacing on its shoulder is fired?


    • Bart – With minimal headspace, like when using a correctly fireformed case, the shoulder will center the case/bullet in the chamber. Of course we are assuming that the chamber is aligned with the center of the bore also.

      Duane Siercks
      Ballistic Technician

      Liked by 1 person

      • Bart Bobbitt says:

        Duane, thanks for responing.

        Are you saying “minimal headspace” to mean the distance from the bolt face to the case head?

        I’ve always thought “headspace” was the distance from the bolt face to chamber shoulder reference diameter. That’s been the industry standard for decades as defined in SAAMI’s glossary of terms. “Head clearance” is SAAMI’s term for the space between the bolt face and case head with the case full forward in the chamber against its stopping point.

        Do you imply that a case that has .003″ or .004″ space between its head and the bolt face won’t center the case neck and bullet in the bore when fired?


      • Bart – I am talking headspace. From bolt face to shoulder datum line.

        Duane Siercks
        Ballistic Technician

        Liked by 1 person

      • Bart Bobbitt says:


        Thanks for the clarification.

        I asked about cases a few thousandths shorter in head to shoulder than the same dimensiion in a rifle chamber.

        All my bottleneck chambered rifles’ reloaded cases center perfectly up front when fired. Doesn’t matter if they’re .001″ or .007″ less in “case headspace” than chamber headspace. With full length sized ones as well as new cases. The firing pin drives them hard into the chamber shoulder but the back end may or may not be against the chamber wall at the case pressure ring.


  5. bill scott BA Okla. says:

    When I built my 6.5 creedmoor I could not find new brass in this area. So I built my own out of 243 Win brass. It was quite simple trim the brass about a sixteenth of a inch then with Imperial sizeing lube run the case in a 6.5 sizeing die. I also anneal the cases before I start the process. After you have sized the case trim to length. Then load and fireform. I have used both new and once fired cases and found the case life to be good with both.


  6. Neal says:

    This technique explained here is one I’ve used for years and works very well (and the explanation was very clear and concise I might add). I shoot T/C Contenders in many calibers, many for which factory brass is not available, or in some cases, never was(“wildcat” loads for instance).


  7. Roger says:

    If you dip the case neck in graphite before final neck sizing, you can gauge how far down the sizing die has to go.


  8. I have been having an adventure fireforming .257 Roberts to .257 Roberts Improved. I’d like to note that with the round shouldered AI chamber, the firing pin has a tendency to push the parent case forward during fireforming. This has been a challenge to correct since the chamber throat on my rifle is long. I tried the technique explained in the article using a .284 mandrel in my sizing die, then neck sizing just to the point where the round will chamber. This didn’t help much. Might you have some other suggestions for that issue?

    The primers stick out around.001 to.004, up to .009 in the worst cases. Is there any way to re-form them to the correct length?


    • John, There is a possibility you may have a slight headspace issue with the rifle, or possibly a headspace issue with the brass from head to shoulder, or a combination of the two. I think I would have the headspace checked by a gunsmith. If that is good, then I would fireform using a 117 grain Pro-Hunter (Flatbase) #1640, and seat it out long enough that it is jammed against the riflings. That will help to hold the case head against the bolt face while fireforming and form a better shoulder as well. Gary Prisendorf, Ballistic Technician


      • Thanks Gary. Since it’s a vintage 1903 Springfield sporter conversion, I’m learning a lot as I go. BTW: When I loaded some 90 grain Blitzkings over 42 grains of IMR 4064, it printed amazing groups, but with more flyers than I’d like. It could be me, but I’d like to make sure the case forming issue is not a factor creating the flyers.


      • Eugene V. Lenarz says:

        Would you please recommend an appropriate powder load when following that procedure? I’ll be forming .257 AI from .257 Roberts +P. Thank you


  9. Phil Yoder says:

    I am certainly not the sharpest knife in this drawer so I fail to see the difference between neck sizing and fireforming. I get the new brass part but once fired it should expand to chamber dimensions. In which case the brass should only need to be neck sized and trimmed to length. Please set me straight. thanks.


  10. Bart Bobbitt says:

    For what it’s worth, full length sizing of fired cases has become the norm in benchrest competition for the last few years. For high power rifle competitioin, best scores have been shot with full length sized cases since the late 1950’s.. Minimally done with the right die, sized cases end up with their necks best centered on the case shoulder. If the die’s set to bump the fired case shoulder .001″ to .002″ back, there’ll be ample head clearance for the case to not bind up the bolt so it goes into battery exactly the same for each shot. Such cases center necks, and therefore bullets, best in the chamber/bore when the case shoulder centers in the chamber shoulder. Doesn’t matter how much clearance there is between case body and chaamber wall; it’s very even all the way around. The back end of the case at its pressure ring may or may not be against the chamber wall at that point.

    As far as I know, Sierra’s still full length sizing all their cases used to test their bullets in. I was told a couiple of years ago Sierra uses Redding full bushing dies for cartridges theiy’re made for,and Redding standard full length sizing dies for the others.

    More often than not, rimless bottleneck case necks get set back a bit when the firing pin smacks them. I’ve had .308 Win case shoulders set back from .002″ for brass ones, .007″ for nickel plated ones. Hatcher reported in arsenal tests that the .30-06 case shoulders often set back .007″ from firing pin impact. Priimers end up pushed out past the case headd. This happens when loads are more than aboiut 10% below max. There’s not enough peak pressure to push the back half of the case so the head stops against the bolt face.


    • That’s really great information.

      I will be investing in a custom full length sizing die as you mentioned at some point. A friend also recommended I do that.

      The firing pin in my rifle is very strong. It’s hard to get the bolt reassembled after I take it apart. I plan to trade this spring out for the much softer spring in my other 1903 to see if it helps.

      It sounds like as I raise the charges in my loads that the added back pressure will address the primer protrusion. I’m just slightly concerned about case life from the body being stretched a bit. I’m hoping that by annealing the necks after the initial fireforming that will help make the shoulder get into the correct position with less stretching of the case body.



      • Bart B says:

        I think the best die is one from Forster they’ve honed its neck out to .002″ smaller than a loaded round’s neck diameter. Or one from RCBS or Redding your ‘smith should do. Several dozen reloads per 308 Win case is normal.


      • Bart B. says:

        Regarding your firing pin spring…….

        Springs weaker than M1903 specs of 16 pounds (force on the pin when cocked) won’t detonate the primers uniformly. Muzzle velocity drops a little and has a greater spread about its average.

        Compare that to springs for the Win 70 of 23 pounds and Rem 700 of 24 pounds and I think their firing pins weigh less than the M1903’s do. Competitive shooters often use springs 10% or more stronger to ensure uniform primer performance.

        Source for new springs:

        Liked by 1 person

  11. Ray Grigsby says:

    Much easier with a properly chambered “improved ” caliber as the native cartridge brass will get a ~0.005″ crush fit on the neck/shoulder junction as the bolt is closed. This keeps the case head firmly against the bolt face no matter how the bullet is seated. I would also say based on my experience with Ackley Improved calibers to use a max load of a faster powder for the original cartridge. Slower powders or lighter loads do not give clean forming and result in split cases during forming.
    Great article 😊


  12. Brad says:

    Good article, but why Fireform 6.5-06 from 270 brass or 30-06 brass? You should be able to resize 30-06 to 270 and then right down to 6.5-06 or 270 down to 6.5-06. Leave the necks long and trim to required length for the 6.5-06 chamber after sizing. The new 6.5-06 brass should fit the chamber just fine without fireforming…I would not waste bullets or powder or primers fireforming the 6.5-06…just not necessary.


  13. Daniel Johnson says:

    Hi I loaded bullets for a Sako 6.5×55 chambered bullets removed .001 / .002. /. 003 The problem when I fired some rounds the primer popped out check all load data again and I was correct for the rounds . The brass cases were once fired . Sound like a pressure problem . But what else could cause this problem ?


  14. Steve says:

    This is an excellent article and very well written.
    I have fire formed many casings from .280 Remington/7mm Express Remington to .280 Ackley Improved 40 degree shoulder.
    I used the procedure of expanding the necks to .308 and then back down to .284 and fitting snug to my chamber set up for the .280 Ackley Improved so that a cartridge causes a firm close on the bolt action. I looked in the loading data and found that a healthy charge of H450 behind a 140 grain bullet would perfectly form the case every time and within 0.001 of spec on my case mike.
    I used the H450 because it is the equivalent of H4831 but spherical and meters very consistently.
    I use my Dillon RL-550 press to make up loads in groups of 100 then take them to the range to fire. H43450 or H414 would also work as they provide good volume of charge for this casing.
    This procedure as produced about 500 well formed cases from not only previously fired brass but also from new cases and those included Winchester Nickel plated.
    These were all done 10 or 15 years ago when there were no commercially produced .280 Ackley Improved cases available from Nosler. I have since purchased some of the Nosler cases.
    In the future as i complete fire forming the remainder of my .280 Remington brass, I will switch to flat base bullets. All of the fire forming so far was done using Nosler Solid Base or Ballistic Tip bullets which have a slight boat tail.
    Thanks again for a great article. I have added it to my library of information.


  15. Steve says:

    I have a further update on my last posting. My rifle is a Ruger M77R with sporter weight barrel originally chambered for .280 Remington. As originally configured I found that the rifle had a long throat. When the rifle was re-chambered in the 1990s, they used the standard .280 Remington/ Ackley Improved 40 degree reamers and kept the long throat.
    One thing that needs to be understood about P. O. Ackley and his Improved cartridge designs is that he set the headspace on the junction of the neck and shoulder and not a data line on the shoulder. I believe he did that because the 40 degree shoulder is so short and it would probably headspace better on the neck/shoulder junction. That is probably why you see that the SAAMI headspace gauge and the original headspace gauge both fit a chamber that is cut with the correct chambering reamer.
    As I mentioned in my last post, I have fire formed several hundred casings using the method I detailed. Any and all .280 Remington/7 mm Express Remington brass fired in my improved chamber have formed correctly with no signs of pressure or flattened primers.
    I purchased two boxes of Nosler factory loads for the .280 Ackley Improved in both 140 grain AccuBond and 160 grain Partition. I have fired them in my chamber and there are NO pressure signs or flattened primers. I have a box of new Nosler brass for the .280 Ackley Improved and I am sure they will chamber and fire properly without flattened primers since they factory loads were built on the same cases.
    If the headspace is set properly there should be no problems. I do have a set of the Redding dies for the .280 Improved as that was the only standard dies available at that time. Custom dies would have required a fired casing and a chamber cast I think for the dies to be built.
    In any situation of resizing brass, if you set the shoulder back on a case when you resize it, you could create excess headspace which would then have case stretch and even flattened primers even with starting loads.
    Thanks for responding to my postings.

    Liked by 1 person

  16. david ambrose says:

    Thanks for all the good info. I have a 6.5mm Gibbs. I had to discover a lot of things by trial and error. I start with Remington .270 brass. Remington already anneals their brass, and I haven’t had any shoulder splits, as I have with other brands.

    I found that when necking down to a smaller caliber, you have to either turn the neck, or ream it from the inside. Turning the neck worked best for me. It also improves accuracy.

    But, I’m curious, why use a flat base bullet over a boat-tail?


    • David – Depending upon the throat length of the firearm, sometimes you need the extra bearing surface length so that you can seat the bullet out further and still maintain enough bullet within the neck to get uniform results.

      Duane Siercks
      Ballistic Technician

      Liked by 1 person

  17. Bobby Skowronski says:

    Having a rifle built on the 6.5 X 55 GWI cartridge. Any suggestions on fire forming this case? It seems to be a simple fire forming process given the case length and bore diameter are identical to the parent 6.5 X 55 SW cartridge. I am sure my gunsmith has a plan and Kelby also has information just curious to read Sierra’s views as I use Sierra bullets in all my rifles.


  18. Harry Dillaman says:

    Made 243 from 308 and ready to fireform. Thank You very much for your article a great help.I also have a large autographed poster of David Tubbs after meeting him at Pittsburgh NRA convention many years ago. He is a very nice and knowledgeable person. WOW! the things he has done with bullets and shooting.


  19. Peter says:

    What if I hand seat paperpatch bullet in 577/450 Martini fireformed cases?

    Liked by 1 person

  20. Patrick Ballensky says:

    Why not use 25/06 cases necked up to 6.5 in 6.5/06 FL. sizing die and be done ?


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  23. Eugene Lenarz says:

    Question: Will fire forming the case going from .257 Roberts to .257 Ackley shorten the neck of the case?


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