Case Trimmers, Cutting Your Brass Down to Size

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Using cases more than once means sooner or latter having to reduce their dimensions. That's when case trimmers such as this RCBS Universal Case Prep Trimmer comes into play.
Using cases more than once means sooner or latter having to reduce their dimensions. That's when case trimmers such as this RCBS Universal Case Prep Trimmer comes into play. Photo courtesy Massaro Media Group and JNJphotographics.

Brass is the one reusable component from ammo, but sooner or later they'll need to be cut down to size. This is when case trimmers become a necessity for reloaders.

In the reloading world, we are faced with a set of dimensional specifications that are prescribed by SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) and life goes much easier when we adhere to these dimensions.

The brass cartridge case that we use is the only component of the equation that is reusable, and that is because it is constructed of a malleable metal that can be resized and reshaped. Those very attributes of the brass cartridge case that make it a good choice for a reusable material see to it that we must trim that flowing, moldable material as it flows and stretches.

So, how do maintain these dimensions so that everything works well once we’ve reloaded our cartridges?

Well, there are a few tools that will make your life easier. The goal, simply stated, is to reduce our brass cases to a particular overall length, specific to each individual case. This overall length dimension is available in any good reloading manual, and you’ll need a micrometer to measure the cases. I like to trim my brass cases to the dimensions specified by SAAMI. This keeps things consistent with new brass.

You’ll need some sort of means of trimming the case, be it a hand cranked adjustable devise, or an electric motor driven machine. I use several different methods, some inexpensive (yet fully functional) and some on the expensive side of things.

Case trimmers can be as simple as this hand-operated model by Lee.
Case trimmers can be as simple as this hand-operated model by Lee. Photo courtesy Massaro Media Group and JNJphotographics

The Lee Case Trimmer uses a lock stud, shell holder, cutter and hardened length gauge; the length gauge is specific for each caliber. Depending on where you shop, you can get into this product for less than $15, and the tool can be used either by hand or chucked into a hand drill for quicker trimming. The length gauge has a pin which uses the flash hole as a guide and stops against the lock stud, so the cases are trimmed to a uniform and correct length every time. Although inexpensive, I’ve used this tool in many different calibers for decades.

Lyman, RCBS, and other companies make quality trimmers that utilize a hand crank to trim brass to length. Some are micrometer adjustable, and most come with caliber specific pilots that help hold the case in place to ensure a squarely trimmed case mouth. Once you set the depth to the desired length, all it takes is a few turns of the crank and your case is trimmed to length. The hardened steel cutters give a lifetime of service.

The Trim-It case trimmer is another neat little gadget that can deliver very accurate results. This trimmer works with a cordless drill or drill press to quickly and efficiently trim your brass. It is fully micrometer adjustable (each notch represents approximately 0.002”), and uses the case shoulder for support. The unit uses case specific dies that can quickly be mounted within the body.

My favorite tool, by far, is the RCBS Universal Case Prep Station. It is an electric motor driven trimmer (no more blisters!) unit, with adjustable rpm dial, and caliber specific collets. The length is micrometer adjustable, and the spring loaded jaws hold almost all rim sizes (although I found today that the big 50/90 Sharps is too big).

When using a case trimmer the micrometer becomes your best friend.
When trimming cases, the micrometer becomes your best friend. Photo courtesy Massaro Media Group and JNJphotographics.

Hands free trimming is a wonderful thing, and the consistency is pretty solid, within 0.002” or so. Another nice feature of this machine is the six rotating heads on the top, which hold chamfer and deburring tools, as well as large and small primer pocket cleaning brushes. Sure saves the fingers and wrists!

Some manuals recommend trimming the cases to a dimension 0.010” shorter than the SAAMI specification. This is fine if you choose, yet not necessary. If you do choose to adhere to the shorter dimension, just remember to trim any new, unfired brass before you load it, to keep things consistent.


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