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.
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 Accurateshooter.com 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!
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.
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.
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!