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Bullet

If you’ve been around guns for any period of time, chances are you have heard of the term “Bullet setback.” If you haven’t, this term simply refers to the bullet being pushed further down in to the cartridge, thus shortening the size of the round, or the cartridge overall length (C.O.A.L.). Why would this be a problem? Shortening the length of the round causes a change in the internal case volume of the cartridge, resulting in higher-than normal pressure upon firing. In drastic cases, this rise in pressure can cause the round to exceed the safe limits for the cartridge.

Some would use this as a talking point against reloading your own ammunition when the truth is that it can happen with factory ammo as well. The primary cause for bullet setback is chambering the same round multiple times, such as in defense-carry, or conceal-carry pistols. Many times, when storing the pistol away, the magazine is removed, the round in the chamber is cleared and then placed back at the top of the mag, causing it to be the same round that is chambered the next time the gun is loaded.


Detecting Setback

For the reloading process, checking a round for setback is simple. One the cartridge is completed, perform a bench test, or “press test,” and measure for setback. This is done by first measuring the length of the round. Then place your thumb on the nose of the bullet and press the round down into your bench and then measure the round again. If the second measurement is shorter, your round has setback.

A second, more definite check, would be to simply chamber the round and measure, seeing if the length is shortened. This test, however, is best done on a cleared round, meaning one with no primer or powder. If you choose to use a live round, it’s best to do so at the range.

Having slight setback, slight meaning a few thousandths of an inch, is normal. However, is you are noticing around 0.010” of setback after one chambering, there’s a problem in your process that needs correcting.

Causes for setback

There are several potential causes of bullet setback. If you are experiencing it, look at one, or all, of these causes.


Sizing Die not properly set

Most cases of setback are caused when the sizing die, particularly those for tapered rounds such as the 9mm. Since these dies are also tapered, they will only properly size the round when the case is inserted fully into the die. If too large of a gap is left between the die and the shell holder, the cartridge will not be sized correctly and be prone to setback.

Pistol could cause it

Setback occurs when the slide pushes the round against the feed ramp on the barrel. If you have a reloaded cartridge that passes a bench test but gets setback when cambered, it could be a problem with the gun. To check this, load a factory round and see if setback occurs. If so, the problem is with the gun. If no factory ammo is available, load the round into a different pistol; if no setback occurs on this gun, the problem is with the original gun.

Undersized Bullets

Though it is unlikely, your bullets could be too small in diameter. To determine this, simply measure a batch of bullets.

These are just a few of the causes of bullet setback. If you realize you are having an issue with setbacks, cease all reloading and determine the problem before continuing. This will ensure your safety and continued success.