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Reloading Basics - Keeping the variables in check

Reloading Basics - Keeping the variables in check

Having considered each of the components required for the reloading process, it is time to look at some of the variables that come into play when you start to put them all together. These variables all influence how your loaded rounds will perform in terms of safety, consistency and accuracy.

Cartridge Overall Length

Reloading data will always state a minimal length for the completed ammunition, usually stated as the minimum Cartridge Overall Length (C.O.L.). The main reason for stating the minimum length is this: The deeper the bullet is seated, the less space is left inside the case to accommodate the powder charge and the gases generated when the round is fired. If the amount of space that the rapidly expanding gases have is reduced, the pressure generated will increase substantially. Taken too far, this increased pressure will reach dangerous levels and can potentially damage both gun and shooter. With only one exception, you should always follow the recommendations of the reloading data when it comes to minimum COL.

This one exception is when the bullet in a round that meets the stated minimum COL in the reloading data actually engages into the rifling when the round is chambered. You should always try a completed round in your rifle to ensure that it cycles and chambers correctly. It goes without saying that this should be done on the firing range in a safe way and not at the reloading bench! If you feel resistance when you chamber a round, immediately eject it and examine the bullet. If it has engaged into the rifling, you will see small shiny ‘notches’ into the sides of the bullet. You may well be able to force this round into the chamber, close the bolt and fire it, but that is not recommended. With the bullet embedded into the rifling, as you fire the round, the rifling will resist the bullet’s movement forward until the pressure increases sufficiently to overcome that extra resistance. The increased pressure can get to dangerous levels before the grip of the rifling is overcome. Just how big the gap should be between the bullet and the beginning of the rifling is debatably, but certainly, when you start reloading, you need to ensure that your bullet is not in the rifling.

If you do find that ammunition that is made to the stated COL engages into the rifling, then you may seat the bullet very slightly deeper, until it does not hit the rifling. This can be done by experimenting with a dummy round, with no primer or powder inserted. Simply keep trying the round in the gun and adjust your bullet seating die by a quarter turn each time until the round chambers easily and the bullet is not marked by the rifling. (TIP: colouring the bullet with a black permanent marker each time will make it easier to see rifling marks on its surface). Extreme care needs to be exercised when doing this because, as explained above, reducing COL also increases pressure. If you are following the instructions that come with your reloading data, and starting well below the maximum load, you can reduce the COL slightly and stay inside the safety margins. In both of the larger calibres I shoot, a 1mm reduction in COL causes a 4% increase in pressure, so be careful!


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The amount of crimp applied to a round will also impact on the amount of pressure that is generated within the case. In simple terms, the heavier the crimp, the higher the pressure. This is because with a heavier crimp the case holds on to the bullet tighter and so it takes more pressure to break it free, to start its journey up the barrel. You can experiment with crimp to see what works best. With too little crimp, you risk the bullet slipping back into the case during chambering, causing dangerous pressures. With excessive crimp, the resulting chamber pressure may be too high and you also risk damaging the bullet, which will in turn affect accuracy. During the crimping process, you are effectively squeezing the case onto the bullet and with excessive crimp you can squeeze a permanent ‘waistline’ onto the bullet. This, combined with the case neck springing back away from the bullet when you release it from the crimp die, can result in the bullet being loose and moving back and forth slightly in the case neck and inconsistent results from the finished ammo. It is well worth experimenting with empty cases, to see clearly what a heavy crimp looks like.

A lot of bullets, particularly jacketed bullets, have an inbuilt crimp groove or ‘cannelure’ around them into which the case mouth rim is crimped. This gives a great guide to the correct seating depth for a particular bullet but COL should always be checked for compliance with the reloading data figure.

In order to check that the amount of crimp is sufficient to hold the bullet securely, a simple test can be carried out. Seat and crimp a bullet into an empty case. Hold the dummy round by just the case and press the nose of the bullet against a flat surface with sufficient force to make it hard to grip the case with your fingers. If the crimp is insufficient, the bullet will be forced back inside the case. If the crimp holds, then it will withstand being chambered no problem.


Reloading is all about keeping the variables in check, making ammunition that performs consistently and safely. Once you have established a Cartridge Overall Length, write it down, or even better still, make up a dummy round and keep it safe. The dummy round is particularly useful if you load more than one bullet weight in the same calibre, as it will speed up resetting the bullet seating die to the proper length. Marking the die body and the bullet seater screw, so that you can line the marks up again if they are moved out of alignment is also useful. The same applies to the crimp, once you are happy with it, mark the die and don’t adjust it. With COL and crimp sorted, your home loads should perform more consistently and accurately, two of the most easily controlled variables dealt with.


Norman Clark Gunsmiths. normanclarkgunsmith.co.uk
Henry Krank & Co. henrykrank.com
JMS Arms. jmsarms.com
1967 Spud Reloading Supplies. 1967spud.com
Hannam’s Reloading Ltd. hannamsreloading.com


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