Trimming Cartridge Casings

Trimming Cartridge Casings

Depending on how new you are to reloading, you may have heard people talking about case trimming and found yourself wondering what all the hubub’s about.  In its simplest terms, case trimming can be described as the process of removing material from cartridge casings to reduce them to a uniform length.

The incredible ‘growing’ case

Now that you know what it is, you’re probably wondering how brass gets to be too long in the first place.  Brass is a relatively soft metal, which is one of the reasons it works so well in cartridges, by allowing them to expand and seal the chamber during firing.  Unfortunately, this same property also makes any case with a shouldered body design susceptible to stretching.

Every time a rifle cartridge is fired, the intense pressures generated cause the brass to ‘flow’ forward, slightly stretching the case.  Although the change is very small, over time it can lead to significant differences from the original specifications.  This in turn leads to inconsistencies between cartridges which can affect accuracy. Even more critically, a case can eventually become so long it no longer chambers properly, increasing the risk of feed issues or catastrophic malfunction.  Because of these challenges, the vast majority of rifle reloaders trim their casings in order to bring them back to factory spec.

Pistol Brass

You’ve heard me mention rifle brass several times now, but what about pistol casings?  While several manufacturers do offer tools for trimming pistol brass, the need to do so is debatable.  As the vast majority of pistol cartridges are straight walled designs with no shoulder, they really don’t flow much.  I’ve been reloading for more than 15 years, and to date I’ve yet to see a single pistol casing that was over length.  For that reason I don’t bother to trim mine, nor have I met anyone who does.

Time for a trim?

How often to trim your brass is a matter of personal preference; some folks only do so after several firings, others make it a habit to trim before each reload.  My .223 cartridges are primarily used for recreation, so I generally only trim them every two or three firings.  Conversely I use my .308 rounds for long range practice where accuracy is paramount, so I trim them every time they’re reloaded.

When in doubt, the easiest way to confirm whether a case needs trimming is to just drop it in your trusty case gauge.  It takes almost no time at all, and eliminates all the guess work from what can otherwise be a tedious process.

In two upcoming articles I’ll be reviewing a pair of different case trimming tools from Lee Precision, and Frankford Arsenal.

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