First of all the article will not be only about full length sizing but also about other types of sizing. Basically there are three ways of case sizing that you can do. First and most common is full length sizing with the exact procedure that is written in the instructions of your dies. Second is neck sizing that got the fame of being the best of both and finally there is full length sizing done right.
Full length sizing to factory specs
This is definitely the most commonly used way of sizing rifle cases. And there is absolutely nothing wrong with this method. Full length sizing to factory specs is also described in the instructions of your full length sizing dies.
Basically what this method does is that it brings our fired cases to factory specifications. This way this cases can be used in every rifle of that caliber. And it is definitely the only way if we have cases that were not fired from our rifle or we don’t know in which rifle exactly we will fire them. So basically we are trying to avoid hard bolt closure or maybe even that the bolt doesn’t close at all.
Cases full length sized can be used in every rifle of the given caliber.
With every resizing we are overworking the brass. Basically we size it more than is needed. We also throw away the stamp of our chamber.
If you still practice neck sizing I strongly recommend you to stop doing it. There are more reasons why you should stop doing this. Let’s see some of them. Definitely the biggest reason is that eventually after some firings you will have to full size your cases.
Why is that? Because after every firing the case is growing bigger and eventually it will be big enough that our bolt will not close easily or even worst it will not close at all. So now please explain to me how a procedure that sooner or later needs full length sizing is more uniform or more accurate? It is not. It can’t be.
There were myths that neck sizing preserves case life. Actually it doesn’t. Since the brass is getting bigger and bigger also the primer pocket will get bigger, to the point where it won’t be useful any more.
It can produce better accuracy then full length sizing to factory specs.
Case dimensions change from shot to shot. Eventually we need to full length size. Sooner than later we will loose our primer pockets.
Full length sizing done right
This is the best procedure of resizing the brass to have same case specs before each firing. This procedure applies only to cases fired in the same rifle that we will reuse them.
Most of people think that for this method we need competition dies or some kind of custom dies. It is not true. Every full sizing die (standard or custom) can be used for this procedure. Basically what is the difference between full length sizing to factory specs and the one that I will describe now.
Let’s first see what happens to a case when it gets fired in our rifle. To make it short a case after firing is a print of our chamber. This is something unique to each rifle chamber. There are not even 2 chambers that are the same. So why throw away this precious data if we want to have the most precise ammo for our rifle? We throw this away by full length sizing to factory specs. If we want to use this data in our favour and do the sizing right we will have every time same case dimensions unique to our chamber that will produce the best accuracy possible.
Measuring case dimension from base to shoulder
The question now is how to do it. First we need a good calliper. Preferably digital that can measure at list .001” accurately. Next we need some comparators. The comparator allows us to measure the case dimension from base to shoulder. This data is important because we want to size the brass in a way that the shoulder is just slightly pushed back. I recommend pushing the shoulder back .002-.003” for a bolt action rifle. This will still ensure smooth bolt closure and will keep our case to almost chamber specs. Important note: the measurement is something that is unique to our case and gauge. A different gauge will produce a different measurement which is not wrong, but it is just different. What this means is that this measurement is not something that we can share because it will not produce the same results.
Procedure of sizing
First we have to take a few cases and measure them. We write down the numbers and then take the approx. measurement as our guide. This measurement is the starting point. From this measurement we subtract .002-.003” and we start sizing the case. The die has to be slowly threaded in the press so that at a certain point we start sizing back the shoulder. Every time we measure the case to see when this starts happening. The procedure seems difficult but it is not. Even if we screw the die in too much the worst thing to happen can be that we get the case to factory specs. This will also become easier and faster when we learn how to do it correctly.
When we finally see that we are at the correct specs we need to stop and secure the die so that it will not move. It is also ok to measure some cases later during the procedure to ensure that the die didn’t move.
We have cases that we flawlessly feed in the chamber with only the necessary amount of sizing. Case dimensions are the same shot to shot. This is specially important when the first shot counts.
Cases resized with this method can only be used in the same rifle.
As you already found out for full length sizing done right we need a headspace gauge. There are quite some of them available on the market. Anyway I would like to give credits to two manufacturers.
Hornady Lock-n-load headspace kit
The Hornady kit comes with 5 gauges and a calliper adapter. This covers most of the modern calibers and is relatively cheap. I would suggest you to buy this kit if you are reloading more different calibers. Even if you only load for one or two calibers you can get just the needed gauges from Hornady.
Whidden headspace gauges
One of my favourite die producers is definitely Whidden Gunworks. When you buy their custom dies you already receive their shoulder bump gauge in the kit. This is exactly to do the full length sizing as I have described it before. Anyway if you already have your dies and you just need a headspace gauge you can get it from Whidden. Their headspace gauges are from one peace and ready to be mounted on the calliper. You can get them for all kind of calibers.