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Overall Ammunition Length Part 2

Overall Ammunition Length Part 1

Over-all-length (OAL) is often one of the easiest, yet most misunderstood, factors of optimum accuracy when reloading your own ammo. Most reloading manuals will show you the OAL for every caliber, yet will give you only one setting per caliber; that setting will be the industry standard, or the SAAMI spec, for that particular cartridge. However, not every gun will have the same bore spacing.


Finding the optimum OAL for your particular rifle requires a bit more information that what you will find in reloading manuals, and that’s what causes the confusion. What’s important to remember before we get started looking at OAL is that when you change the length of your round to fit your own rifle, that round most likely will not work in another rifle. Also, changing the OAL might affect how the round loads into a magazine.

Setting the OAL to fit your particular rifle is perhaps the cheapest improvement there is in terms of accuracy. However, lengthening your round will also increase chamber pressure. To understand why that is, let’s look at this example. A car can easily drive over a curb when it has a running start. However, if you park your car against the curb, it will require more power, or pressing of the gas pedal, make it over the curb.

Increasing the OAL will put the bullet closer to the rifling on your barrel, in turn requiring more power to be behind the bullet for it to start down the barrel. Keeping this in mind, when we begin to increase the length of the round, we must work up the loads slowly and gradually. The benefits outway the risk when you consider that the optimum length of accuracy in lengthened rounds will almost always be longer than that of factory ammo.

When increasing the overall length of your round, you must remember that it’s not the tip of the bullet that comes in contact with the rifling; it’s the side of the bullet. Therefore, measuring the optimum length isn’t from the tip of the bullet but rather the side. Finding that length is easy, but does require a little ingenuity to make it simple and accurate.

Using a casing that has already undergone the resizing process, use a Dremel tool to cut 3 to 4 evenly-spaced slots from the tip of the casing to the bend in the shoulder. This provides a way to hold the bullet securely yet not so strong as not to allow movement when chambered in your gun. Don’t worry; you won’t be firing this round.

Using this “slotted case tool” you’ve created, place a bullet at the end but do not press it down. Then, carefully and slowly chamber the tool and bullet combo into your gun. The rifling on the barrel with ush the bullet into the slotted case. Then, once the case has been completed chambered, carefully extract the case without moving the bullet. Now, you can measure form the side of the bullet to the bottom of your case and you have the exact measurement for how long a case can be and still fire in your gun.

Now that we’ve looked at finding the length of the case, part two in this series will look at adjusting this length to find the optimum OAL for your rifle and how to manipulate that to find the most accurate shot possible from your firearm.