Precision Reloading – Brass Resizing Methods

In Blog by Rich40 Comments

Here’s a reloading topic that comes up quite a bit when discussing Precision Reloading: Full Length Sizing Vs Neck Sizing Brass. What’s the difference between them and which is better? We’re going to cover those questions along with an explanation as to the precision reloading process on both sides. The main things you have to keep in mind when deciding what method to use when sizing your brass is what your ultimate goal has become. Are you looking to get the absolute longest life and longevity out of your brass or are you looking for a more consistent preparation of the cases. Full length sizing will generally offer the best reliability and consistency while neck sizing offers better brass longevity.

Precision Reloading: Full Length Sizing

When full length sizing your fired cases you are doing just what it sounds like. Each time you size a case you are re-sizing the entire case including the body, shoulder, and neck. This tends to be the more popular option for the tactical rifle crowd for one reason, reliability. If you size every case back down to standard case dimensions there is no doubt as to whether the loaded cartridge will chamber and feed properly. While you may get better brass life by neck sizing, just how much better is up for debate. A properly configured full length sizing die will only move the shoulder approximately 0.002″ of an inch. The rest of the case dimensions like the neck and body will be sized back to original specifications.

The reason full length sizing can be harder on cases is because when a primer is ignited the case swells up inside the chamber and expands outward until the chamber wall stops it. Since the brass can no longer expand the growing pressure within the case then pushes the bullet out of the case and down the barrel. After being fired the brass will “spring back” slightly from the chamber’s dimensions. Otherwise it would be hard to extract and eject the case. Depending on the chamber it may be close or not so close to the actual cartridge specifications. The greater the difference, the more the brass has to expand and grow to fill the chamber.

When you re-size the case you essentially take it from having been “fire formed” to the inner dimensions of your chamber and you are sizing it back down to the cartridge specifications. Typically the area of the case that suffers from the constant expansion and re-sizing of the brass is just forward of the case head. Over time the brass will start to grow thin forward of the case head where the brass is continually stretching to expand and allow the neck and shoulder to move forward and fill the chamber. If you don’t set up your reloading dies properly, and you are moving the shoulder back farther than about 0.002″ you are overworking your brass.


This is a bent paperclip that can be used to check for thin spots on the case wall by gently scratching the interior of the case where you see it in the cutaway, this case is fine by the way!

The idea is to move the shoulder back 0.002″ to ensure reliable chambering, extraction, and ejection, and nothing more. This way on subsequent firings the brass only has to expand that same 0.002″ to fill the chamber. That means less work hardening of the brass, less trimming of the cases that needs to be done, and better brass longevity. If you size it all the way back down to spec then the brass is growing more than it needs to every time you fire it. Eventually the brass will develop an impending case head separation. If pushed too far, the case head will separate from the body and you will potentially have hot gases venting into your chamber that may damage the gun.

There is an excellent article over at about case head separation that you should have a look at for the photo alone. I didn’t have any impending separations to show you but the photos on that article are excellent. They show what you are looking for and what you want to avoid. Remember, if you have a batch of brass that is getting long in the tooth and you are starting to see signs of possible separations or you aren’t sure how much life the brass has left, check it! It takes all of 3 minutes with a dremel. Grab a few pieces from that batch of brass that look the worst and cut a section off and examine them! As the photos above show I had a few hundred cases I suspected were spent that had plenty of life left in them. I hadn’t done as much damage with improperly adjusted dies as I thought. The case above was from the very first batch of brass I bought for reloading!


This brass doesn’t have any impending separation, however, it will look like what is circled on the left, and it will appear on the sides of the case wall where highlighted to the right

Precision Reloading: Neck Sizing

Neck sizing brass has a different process and set of ideas behind it. The theory here is that after brass has been fired it has been formed to your chamber and has sprung back slightly from there. So essentially those cases are now a very good fit for your rifle and will only have to expand slightly under pressure from the next firing to fill the chamber. Rather than make it expand farther, the idea here is a “less is more” approach to re-sizing your brass. Rather than size it back to cartridge specifications, you only size the neck. By just sizing the neck you are only doing a little work hardening on the brass that comprises the neck of the case.


These are a set of Redding Type S Bushing dies for 308 Winchester, while they look the same, they aren’t! The full length die sizes the entire case, the neck die is bigger inside and only sizes the neck of the case

Another benefit of neck sizing is the reduced number of steps necessary to process the brass. Often the experienced hand loader that has embraced neck sizing as a method for sizing his brass, as part of the precision reloading process, can skip several steps that others can not. For example many people who neck size can afford to skip trimming their brass for several firings until the neck grows in length to the point where it becomes difficult to chamber the round. That saves processing time and keeps the shooter on the range and away from the reloading bench. Another benefit as we mentioned earlier is the reduced work hardening of the case because the only portion of the case being sized is the neck.

What about downsides? Unfortunately with neck sizing, there are a few. As mentioned above often a reloader or handloader will skip trimming the brass for several firings. This can save time on the bench but you run some risks with the reliability of your weapon. Specifically if the necks have grown faster or sooner than anticipated it can cause problems with the rounds not chambering properly, or at all. I’ve seen this happen to people and it sucks to be in the middle or even the start of a match and your rounds don’t load properly. You can mitigate this by keeping a closer eye on the length of your cases, but that means more measuring and more time at the bench.

The other potential issue with neck sizing can be headspace, or lack thereof. This really has more to do with the setup of the dies during the precision reloading process than the choice between full length or neck sizing. Just like an improperly set reloading die can cause problems with case head separation for the reloader who chooses full length sizing, it can cause problems for the person neck sizing as well. The problem tends to manifest itself in the opposite direction. If the neck die isn’t being set up to bump the shoulder back eventually the case grows and won’t chamber properly because the length of the case between the shoulder and case head has grown too large for the bolt to close against. The important thing to remember here is that even if you are “only neck sizing” you still have to bump the shoulder or risk reliability issues with the cases chambering, extracting, and ejecting properly.

Precision Reloading: Making the Choice

So which one of these options is better? I think like everything else in this sport, it depends on your purpose for the rifle and ammunition. We tend to stress reliability with “field” or “tactical” applications. It is possible to have a case that has been neck sized, and had the shoulder bumped, that still doesn’t chamber easily. You can also have it fail to “spring back” at which point you experience what is referred to as a stuck case in the chamber. That all has to do with work hardening and how springy the brass remains during its lifespan. For tactical and field applications I think you are better off full length sizing the cases. That ensures reliability of the gun. If you are shooting at a bench, or if you bring reloading gear with you to a square range, you can afford to neck size and save yourself some time and effort.

Wrapping Up

Consider this, you can do both, you don’t have to choose between these two techniques for resizing brass as part of your precision reloading process. Neck tension can have a lot to do with the consistency of your ammunition. How much pressure is required to unseat the bullet can drastically affect the consistency of your ammunition and how tight your chronograph numbers will be. I full length size my cases and bump the shoulders with a full length die. I also run them through a bushing neck sizing die to ensure that the necks are all uniformly sized and have the same tension applied to the projectiles. That may be an extra step, but I’ve had very little trouble finding accurate loads for my rifle with single digit standard deviation and low extreme spreads when I test the ammunition. I’m always interested in hearing about the experiences of my readers, so if you have something to add to the topic or a question, drop it in the comments below!

Owner and Proprietor of AccuracyTech, LLC. Rich is a Firearms Enthusiast, Precision Rifle Competitor, and Writer. He is committed to bringing readers quality reviews and articles related to the Precision Shooting Sports. If you have any questions for him, please use the contact form on the site.


  1. Excellent article which makes my half-finished article on on the subject kinda redundant now ! Anyway, to my question – what are your thoughts on Small Base Resizing for Semi’s and for those bolts that have a tight (match) chamber ? There appears to be some controversy over the issue.



    1. Author

      In those situations it can be very beneficial to use a small base die. I use one for my semi auto 6.5 Creedmoor and it feeds flawlessly.

      I would suggest trying a regular die first and then if a tight chamber is causing problems try a small base die. Just because you have a semi for example doesn’t mean you need a small base die!

      I had some trouble getting my auto loader running smoothly early on so a small base die was a logical step. They really work your brass hard so if it can be avoided, I would.

    2. Great article. Quick question – I’m trying to determine if I should full length size (with minimal shoulder bump) using the Redding FL bushing die or to use the Redding body die then the competition neck sizing bushing die. The latter is an extra step and wondering what value it has? If you set up the dies to bump shoulder the same amount and are using the same bushing what is the difference? I guess one potential benefit of the two step process is to choose how much of the neck is being sized but not sure how much there is to gain by not sizing all the neck. Appreciate any help!!

      1. Author

        For tactical shooting just use the FL Bushing die. There are some who believe there are benefits to working the brass less and neck sizing only but that’s the Benechrest/F Class crowd. I’ve never done it. I want reliable chambering and ejection.

  2. What about not sizing at all? Shooting 7mm rem mag belted cartridge and thinking of not sizing, if the round chambers and extracts smoothly are there other potential downfalls or dangers to not size the brass other than possibly inconsistent neck tension?

    1. Author

      Eventually the case will grow to the point where feeding is problematic or doesn’t happen at all and you will have to trim the cases. It can bring on some pressure problems if you really have to muscle the cases into the chamber because they’ve gone untrimmed too long.

      How long that takes is different for every rifle.

    1. Author

      I have never done it but others have, I believe it’s more commonly done with 270 brass.

  3. Will a properly set up FL bushing die accomplish the same thing as bump die and then NK bushing die?

    1. Author

      Yes, you’re combining operations. A bump die is made just for moving the shoulder back. A neck die just sizes the neck. A full length die will move the shoulder back AND size the body AND size the neck. The nice thing about a full length bushing die is you can set how much it sizes the neck.

      1. Thanks Rich. That’s what I thought too. By the way I just discovered your site a little while ago and I enjoy it yugely. You guys know what you’re talking about. Thanks

  4. What would be the downside of FL sizing on a belted magnum like a 300wm? Just getting into reloading and seeing a lot of guys against it but not so sure why. Any other articles you can point me to where the belts are specifically addressed for the newb reloader?

  5. If I’m reloading on a progressive could I use the lee neck sizing collet die in the first station then in the second use a full length sizing die with the decapping pin and neck expander removed? Seems like this would also avoid having to lube the case. I’m reloading .223 for an AR by the way.

    1. Author

      A full length die will size the neck every time. You can’t get around lubing the case prior to using a full length die or you’re asking for a stuck case.

      If you want to size the neck in two steps I would suggest some kind of bushing/collet full length die in addition to the neck die.

  6. Eddie
    I have done some experimenting with sizing brass for concentricity. I have worked with standard fl die. I also use type S bushing fl die, and I am currently trying a two step process using a body die (I took the bushing and expander assembly out of the type S fl die) and a collet neck sizing die. I first use the body die bumping back about .002 then the collet die, then I trim my cases.
    Well I have found the two step process to work very well, with concentricity in the .001 or less,(measuring at the neck of course). I am not neck turning, and this is my hunting rifle but I do enjoy the reloading process.
    It was my decision to body size first then collet neck size. I just figured thats the way it happened inside a fl sizing die so I went with it.
    I have never just neck sized and shot the round.
    Have you used a multi step process like this and what are your findings?

    1. Author

      I have a multi step process as well and every time I check there is very little runout. I clean my brass first to avoid gunking up my dies. Then I FL size with a Redding Bushing die, no expander unless the neck is crushed or stepped on. This bumps the shoulder and moves the neck roughly halfway to final tension. I clean it a second time with the primer pockets exposed and to remove the sizing lube. Then I run it through a Redding Bushing neck die for final tension. Then they hit the Giraud trimmer. Lastly, I’ll prime, charge, and seat a bullet.

      I typically see 0.001″ or less runout. Occasionally I will see more but it’s usually a case that got stepped on or something when it happens.

      1. Eddie again. So the bushing in your first step with the fl bushing die you intentionally order it to only sizes the neck about half way and later with the bushing neck die you bring it to its final size. ??

      2. I spent a lot of time testing neck concentricity on fired 260 Rem and 338 LM brass (all Lapua, all neck turned to .0135″). I found that:
        1. Typically an uncleaned fired case has neck concentricity < .001"
        2. Concentricity after neck sizing is consistently worse at .004" to .007" – for both calibers. I'm using Redding micrometer dies with titanium bushings
        3. FL sizing with the expander also results in poor neck concentricity similar to above. I'm using a Redding FL resizer.
        4. Removing the expander results in neck concentricity from.0002" to < .002". The expander is clearly bad news!
        5. After FL sizing there is more than enough neck tension – around.005" more than recommended. For cases that have not been neck turned there is too much tension and bullets are damaged while seating.

        Since stopping neck sizing and FL sizing only I have been getting measurably better results in accuracy.

        Two things I have picked up from this article that may improve this are:
        1. Clean the cases beforehand – the FL resizer might be getting gunked up, particularly in the neck area worsening concentricity
        2. Set up the FL resizer to only bump the shoulder slightly. Right now I am setting the die to touch the raised ram.

        I would be interested to hear if anyone has similar findings or thoughts on this.

        1. Granville. I’ve had the same experience with my 308 Lapua brass, Redding dies, consistency etc.. Instead of turning necks and having to mess with the donut I choose to sort brass for a change. Over 75% of my brass measures less than .001 variance neck thickness and 86% weighs within .8 gr. (174.1-174.9). After fired they spin out less than .001 concentric. I had acceptable sizing with the Redding bushing dies and in every configuration possible, and I own them all, but the straightest case AND loaded round come out of a RCBS competition FL sizing die with the expander installed and +.10 Redding shell holder. That gave me .003 headspace, .002 neck tension, and loaded rounds always spun out less than .003 with most between .0005 and .0015 on the Sinclair concentricity gauge. I shoot 185 Berger Hybrid Target or 180 Elite Hybrid out of a stock Savage 10 FCP with HS precision stock. Groups avg. between .300 and .600 at 100 yards with and SD of less than 10 measured with the MagnetoSpeed chrony. I would really love to say that I’ve had my best results with the Redding dies but I can’t. Of course it might be something I’m doing wrong and I’m always open to suggestions. Thanks for your post. It inspired me.

    1. Author

      You can’t. It isn’t set up to touch the shoulder. You will need a bump die that only addresses the shoulder if you are wanting to leave the body alone and use a neck die.

  7. Load Development – Distance from lands:
    Sorry if this is a bit off-topic but I didn’t see a better topic discussion for the above. I’m interested to hear if folks believe that barrel harmonics show up and impact group size when testing a variety of COAL’s to determine a rifle’s sweet spot relative to distance from lands.

    I’m looking at two recent tests and seeing sweet spots at both 0.010″ and 0.020″ with more scatter at 0.015″. Any insights on this would be much appreciated.

  8. I have a Browning A-Bolt in 7MM WSM. I’m reloading the nickel plated cases for it. I FL sized once fired cases and bumped the shoulders back .0015 to .002. I ran the cases thru the gun but they are still snug when closing the bolt. They were all trimmed to “trim to length” and FL sized with bumping the shoulders. I also have a 270 WSM that I load the same way and bumping the shoulders the same amount made the cases chamber easily. I’m using regular Win Brass with that gun. Maybe the Nickel plated Win Brass needs more bump? Any ideas.

    1. Author

      Sounds like it! There are no hard and fast rules, every gun is different and that one may need more bump or even more trimming on the cases. You’ll have to size a few and see what the result is.

      How are you measuring the shoulder bump?

  9. If your net shoulder set back dimension is accurate, the nickel coated cases shouldn’t be a factor. The necessary tolerance is the necessary tolerance.
    However, there may be differences in spring back during the process, so you may not be able to measure a setback for “standard” brass cases and then assume you will get the same result with a nickel plated case. I assume you are measuring your results each time. If you are still having a difficult time closing the bolt on your case with 0.0015″ or 0.002″ setback, you may need to increase until you get the desired fit. Although chamber drawings are pretty precise, you rarely know the condition of the reamer used unless you built the rifle.

    Another factor that should be considered is how many times the case has been resized and fired. The acts of firing, case prep, resizing etc causes work hardening of the brass which affects how the case subsequently responds to resizing. Annealing can help relieve the case hardening and help produce more consistency in sizing operations as well as neck tension.

  10. I am having the same issues with neck sizing my 308 and length trimming also but still getting stuck cases and hard close on the bolt, can you direct me to the info on how to set up a die correctly, measure the case at what points ETC

    1. Author

      You need a shoulder bump gauge, that way you can measure fired cases, and check if your dies are moving the shoulder back the correct amount.

    2. Robert – Rich is correct in that a bump gauge will measure the amount of the shoulder set back compared to your fired case (that forms to your chamber). It’s the best way to actually know what is going on and optimize the shoulder setback. You basically compare a case that was fired in your chamber to one that is resized to understand the differences.

      Typically, most full length dies are set up by screwing the die down to the point where it makes contact with the shell holder when the ram is raised to the highest point. In some cases, it can be adjusted so that it “Cams” over slightly when contacted. Trim your brass AFTER resizing for the correct dimensions listed in a reloading manual.

      If after full length sizing the cases they are still hard to load and close the bolt, you will most likely need further shoulder bump. This can be achieved by custom shell holders (Redding) designed to lower the shell holder height and provide further movement up into the die to push the shoulder back further. Redding also makes custom shell holders that are taller than standard to reduce shoulder bump if you are having excessive headspace issues.

      Please rememmber that what is described here is “general” and basic information. If you don’t have a copy of your specific die instructions, you should contact them and they will provide it for free – most likely they will have it readily available on the web.

      1. Thank you for the info Greg and I watched a few videos to help me under stand a little further on the process. I have all my problems just on neck sizing with hard to close and open bolts. I’m trying to be as accurate as possible and get the most use out of my brass.. I neck size my brass and then trim, so why do I have this problem with fire formed brass and how often should I do a complete resize of the brass.. I did see on one video were I could back my die out to get less shoulder bump but still resizing the full case and this is suppose the be the middle of the road way to go to be accurate and use of brass..I have to buy special little gauges to do this Though ,,,, Still wanting to neck size can you tell me what might be happening with my fire formed cases that have been neck sized and trimmed but are hard to close and open ..

        1. When you neck size only, you are not bumping the shoulder back, you’re only working the neck. As this process is repeated over and over the brass work hardens and doesn’t spring back like it used to. At this point you should have to full length resize (and may also want to consider annealing the necks). They should then chamber and extract easily and then allow you to go back to neck sizing only.
          Backing the die out for less bump is the opposite direction you need to go. You need to use a properly adjusted full length die and make sure it is setting the shoulder back slightly and resizing the case body. When you neck size only and don’t ever resize the rest of the case, you eventually run into the bolt close and hard extraction issues over time.
          Don’t be afraid to full length size – some of the best accuracy can be achieved and you can still obtain tons of case life. I have cases that have been full length sized more times than most would believe! You just need to inspect.

          1. Thank you, always wanting to learn, I can can never get enough education..

  11. So is there any advantage to just using a FL on range pickup or new brass only, then using the neck sizing die for brass fireformed in your chamber (at least until the bolt gets harder to manipulate, then you have to FL again)?

    1. Author

      The advantage is not over working your brass. I recommend FL for reliability, I’ve had brass that wasn’t sized enough at a match and it made for feeding problems all weekend.

    2. I do shoulder bump to get the best of both worlds and it seems to work well if you only have one gun in that chamber “ caliber” if you have two of more you will have to do smallest one so it fits all of them

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