Setting up a Full Length Sizing Die | Top Rated Supplier of Firearm Reloading Equipment, Supplies, and Tools - Colt

Setting up a Full Length Sizing Die

Even if you are neck sizing your cases most of the time, you will eventually need to turn to your full length sizing die when your cases are so tight in the chamber that the bolt will not open or close easily. Full length sizing should be done on a 7/8”-14 reloading press that has sufficient rigidity to handle the load required for the size of the case you are re-sizing. Neck sizing takes minimal effort to change the geometry of the case neck. Full length sizing takes considerably more effort as you are sizing a bigger column with thicker walls (the case body), the case neck, and re-positioning the shoulder (headspace) of the case. More press strength is required as well as additional lubrication. If you are loading for a hunting rifle, semi-auto, or just a rifle with weaker extraction such as most lever guns, we recommend that you full length size. In a hunting situation and some competitions, you cannot afford for a round to not chamber or not chamber easily. The risk of it not chambering versus the reward of longer brass life or slightly better accuracy is not worth it.

When cases are new, it may take a few firings before you need to full length size. It is not unusual to have three or four firings on a case before you need to full length size. How often depends on the geometry of the case, the chamber, the softness/hardness of the brass, and the chamber pressure generated from your load.

When setting up a full length die in a press, the procedure is different than with a neck die. The position of the shellholder when the press ram is fully raised in relationship to the bottom of the full length die is critical to determining the amount of full length sizing that occurs. This position determines how much of the body of the case is sized but, more importantly, it affects how much the case shoulder is set back, which changes the cartridge headspace. The amount of cartridge headspace has an impact on accuracy, ease or difficulty in feeding the case whether from a magazine or loading ramp, and on extending the life of the case. Please read the discussion on “Cartridge Headspace and Over Sizing” in the highlighted section if you are not extremely familiar with this concept.

Cartridge Headspace and Over Sizing
Cartridge headspace can be defined as “how much the cartridge case moves forward and backward in the chamber upon firing when the breech or action is fully closed”. When a chamber is reamed by a manufacturer or gunsmith, there are maximum and minimum dimensions that SAAMI (Sporting Arms and Ammunition Manufacturer’s Institute) specifies for the chamber for a particular cartridge. This dimension determines the fixed headspace of the rifle’s chamber. A thorough and competent gunsmith will check the rifle with “go” and “no go” gages to make sure it doesn’t’ have excessive headspace or insufficient chamber headspace. Excessive headspace can lead to serious problems such as excessive case stretching and most probably case separation/failure. Insufficient headspace prevents the chambering of cases into the rifle. Thus, since each rifle chamber can be machined to fall within a range of the minimum and maximum dimensions for the chamber, you can understand why we don’t recommend using brass fired in one rifle to be used in another.Brass comes from the factory manufactured within its own SAMMI specs. Brass could be made to the maximum SAMMI spec and a chamber made to the minimum spec. This situation might require brass to be full length sized prior to using it.When you full length size a case you are increasing the amount of free space the cartridge has within the chamber. Minimal sizing will allow your brass to chamber properly with little effort. Excessive sizing will also allow your brass to chamber easily but will create excessive headspace. This extra headspace will allow the case to have excessive forward and backward movement when it is fired. This presents three problems for the reloader. One is that the case could fail or separate in the chamber, which could lead to gases blowing back into the shooter’s face. Secondly, the case is work hardened by the excessive sizing and by the movement of the case in the chamber. Lastly, the excessive movement and the chamber not sealing properly can reduce accuracy.

Most die manufacturers have instructions for setting up their dies in a press. These instructions will normally position the die an approximate distance from the shellholder. Usually, these instructions result in almost maximum sizing occurring. They will also have some guidelines for achieving minimal headspace. In the manufacturer’s recommended position, the die will size the cases enough so that the cases will chamber in most rifles. The instructions for setting the dies to a minimal position are usually based on how the sized case “feels” as it is chambered. Using the method of how the case “feels” to chamber is fine but this is preferably done with the firing pin assembly removed from the bolt. If you don’t know how to remove the firing pin assembly from your rifle, refer to the instructions that came with the rifle. Removing the firing pin assembly from the bolt allows you to more easily feel the case as it enters and exits the chamber without feeling the effect of the firing pin spring as it compresses. This method is described in the inset entitled “Feel Method to Adjust Your Full Length Die”.

Feel Method to Adjust Your Full Length Die.
Many handloaders adjust their full length die by the “feel method”. These handloaders adjust their die in the press until it sizes the case enough so the case chambers easily. To do this properly, you should remove the firing pin assembly from your bolt so you can feel the case without the effect of the firing pin spring
  1. Remove firing pin and spring from the bolt.
  2. Back the full length die out of the press so it is away from the raised shellholder approximately the thickness of a nickel.
  3. Chamber a fired case, it should be difficult to chamber. Note the feel.
  4. Rotate the die clockwise in small increments so it moves closer to the shellholder. Try less than 15 degrees of rotation at first. This is almost .003” of downward movement and you may go past the ideal spot.
  5. Size the case and then chamber it to check the feel. If it feels easier, you are close. Try smaller movements of the die. If it chambers too easily, you have probably gone past the ideal point.
  6. If it still feels that it is difficult to chamber, move the die again and size the case. Keep moving the die downward until the desired feel is reached.

A better and more accurate way to setup your full length die is to use case gages commonly available throughout the handloading industry. Sinclair International, L.E. Wilson and Hornady makes tools that you can use to measure the amount of sizing your die does to your cases. The method for using them is described in the highlighted section, “Using Gages to Adjust Your Full-Length Die”. These tools take the guesswork out of adjusting your full length sizing dies.

Using Gages to Adjust Your Full Length Die
The easiest and most accurate tool to use to setup your full length sizing die is the Sinclair Bump Gauge. The easiest and most accurate tool to use to setup your full length sizing die is the Sinclair Bump Gauge. A Sinclair Bump Gauge is a tool mounted to dial or digital calipers that you use to measure a case for length from the base to the shoulder of the case. The Sinclair Bump Gauge consists of the tool body and various inserts for specific cases or a family of cases.Begin with your die the manufacturer’s suggested distance away from the shellholder. This is usually the position for near maximum sizing of your case. Then measure a few fired cases with the Sinclair Bump Gauge (see photo) to establish a baseline measurement from the case head to the shoulder. Then incrementally adjust the full length sizing die away from the shellholder, size a case and re-measure it with the Sinclair Bump Gauge. Repeat this step until you have reached the desired amount of sizing or “bump”, then lock the die in the press.
Wilson Tools makes Cartridge Headspace gages for traditional bottle neck cartridges as well as belted magnums that traditionally headspace off the belt. Wilson gages mimic the chamber of a rifle and have minimum and maximum steps cut into the surface of the gage. You use the gage by holding the gage horizontally and pushing a fired case into the gage with your finger until the shoulder of the case contacts the machined shoulder of the gage. Turn the gage so the case head is facing up. You should be able to observe the top of the case head with respect to the minimum and maximum steps on the gage. A fired case from most chambers will have the head positioned either slightly above or slightly below the maximum step. You can then adjust your full length sizing die and check the case in the gage until it is positioned so the case head is slightly lower in the gage than was the fired case. This position change will be about .002” to .003” worth of sizing. If the case head falls below the minimum step, you went too far, back the die off. The use of a small steel scale or rule is great for use with these gages. If you place the rule on top of the case head and inline with the minimum steps there should be clearance between the rule and the steps unless the case has been oversized. If you place the rule so it rests on the maximum steps there should be clearance between the bottom of the rule and the case head. If the rule rocks on the case head and doesn’t fully contact both maximum steps, then the case is above the maximum headspace.

Hornady (formally Stoney Point) makes a set of Headspace Gauges that attach to calipers. The reloader would use the Hornady tool in a similar manner as the Sinclair Bump Gauge. These gauges do not tell you whether your sized case is between the established SAMMI specifications for minimum and maximum headspace. They indicate the amount of sizing that occurs from a fired case.

Ideally, the amount of sizing you want to have occur for most hunting and varmint rifles is approximately 0.002” to 0.003”. Benchrest shooters and other competitive shooters will normally only “bump” the shoulder back approximately 0.001” so there is minimal case movement in the chamber. The balance that a benchrest shooter tries to achieve is the minimal headspace change he can achieve that still allows the cartridge to chamber without requiring too much effort to close and open the bolt, thus not disturbing the rifle’s position on the rest and sandbags. Some benchrest shooters will not even use a full length die to set back the headspace but will use what is called a “bump die”, which only adjusts the shoulder position and headspace while leaving the body alone. Some of these “bump dies” do have provisions for using bushings to size the neck. This same headspace balance is also important for a position shooter (prone or standing). You want the case to be well fitted to the chamber but you don’t want to have to force the bolt open each time with hot loads and disturb your position and “Natural Point of Aim”.

To adjust the headspace sizing in full length dies, you simply turn the die in or out of the press accordingly. Remember that 1/8 of a turn will result in approximately .009” of vertical die movement and change to the amount of headspace. Some handloaders will set their die up to achieve maximum sizing and then progressively use Sinclair Die Shims between the lock ring and the press head to move the die away from the shellholder. Doing this allows you to leave the lock ring in the same position. These shims are usually available in increments of .001” and work very well. Redding Reloading approaches it in a different manner and has sets of shellholders that are machined in increasing thicknesses to move the case closer to the die without disturbing the die’s position in the press.

Setting up your full length die for the correct sizing amount is a relatively easy task to do, but one that pays great dividends in greater brass life, accuracy, and safety.