How to use a case trimmer?

Can ammo cases be reused? If yes How?

You are in the right place if you are looking to answer these questions.

First, ask yourself, why are you here? 

  • Is it because you want to be more cost-efficient, 
  • Maybe to get to know your gear more personally to tweak for a more efficient and powerful outcome 
  • Maybe it is just a wonderful hobby. 

Whichever the reason, you are in the right place for the answer. But, let me point out at first that contrary to the popular belief, it does reduce cost in the long run.

Is a case trimmer necessary? What is a case trimmer used for?

How to use a case trimmer

A recyclable component of the ammo is the ammo brass case. After firing rounds (single or multiple), the brass case deforms due to the high pressure in the chamber created by the explosion of the gun powder, and to reuse the ammo brass case again you need to resize the ammo case. And to resize the ammo brass case you will need a case trimmer.

All ammo brass case has a length that must be maintained, and if the length is even more than the allocated length, then the case gets jammed in the chamber after firing that particular round. And, if the length is shorter, then that particular round loses power. And, at times can even damage the rifle.

To keep the length of the case in the desired range you need to trim the case accurately to 0.001” (with a wiggle room of .005”, but the more accurate the better) and that is when the ammo case trimmer comes into action.

You have the option either to buy new ammo (which is expensive and is usually avoided by professionals and semi-professionals shooters) or recycle the brass case and reduce cost. And an ammo case trimmer is used to trim the ammo brass case to the desired length.

But keep in mind this is not the only step. This is one of many steps to begin reloading.

Now to the more important question, How to use a case trimmer.

There are a few different ammo case trimmer brands available in the market. You can review the brands and their most sold ammo case trimmer in my other article here. 

The general idea of using a case trimmer is usually the same, except for some handheld case trimmers, where the pilot is provided and no additional length adjusting is required.

Even then there are some differences, and they usually are 

  1. How you set the bushing in line with the blade shaft. 
  2. The amount of RPM (Rotation Per Minute) and torque of the blade – this matters because if the RPM is low the cut will be rough and if the torque is low the blade might just get jammed while trimming.
  3. The accuracy of the desired length to the nearest 0.001”.
  4. The amount of time required for successive brass trimming.

Using a case trimmer is simple. In the following steps, I will try to reveal my understanding curve. However, understanding the major components will make trimming easier, as you will know what went wrong if something does go wrong. 

The power
unit of the system
It is a heavy-duty motor connected to the blade shaft for rotating the blade and trimming the case. Or the hand crank which you use spin manually to spin the blade for trimming the ammo case. The heart of the system.
The trimmerThe trimmer is the blade, which is connected with the motor shaft or hand crank and performs the cuts on the bass case. The arms of the system.
The bushing, pilot, and colletThe housing that holds the brass ammo case aligns with the blade to avoid slanted cuts. This bushing/pilot/collet comes in various sizes for various calibers. The brains of the system.

These are the major components and different brands might include other components, such as chamfer, deburr, case neck cleaner, primer pocket cleaner, etc.

Now to the reason why you are here,

How to use a case trimmer.

  1. Choosing the right bushing, pilot, and collet for the right brass case is the first step.
  1. After bushing selection, insert the brass case through the collet in such a way that the brass case mouth is just kissing the blade and fix the length by either using a stop collar or jammer nut.
  1. Make sure to adjust the pressure by the collet on the case to stops any wobbling, at the same time making sure not to tighten the collet too much, as it will hinder for easy changing of ammo case. (this step is variable depending on the type of ammo case trimmer you use).
  1. Adjust the dialer to make a fine trim length adjustment, usually with an accuracy of 0.001 inches. But the acceptance range of a trimmed ammo case is between 0.001 inches to ±.005 inch of the desired case length. 
  1. Usually to increase length for trimming turn the stop collar clockwise and to decrease case length turn it anti-clockwise.
  1. The bushing, collet, or washer has a lock/stopper system to limit excessive trimming. However, it still takes some trials to get the perfect length. 

Measure the length to check if readjustment is required. It is a good idea to always keep a referenced brass case for faster setting arrangements. 

Please note that these is the general steps. And can slightly differ from brand to brand. Hence it is a good idea to always read the manual provided with the product.

If things are in order, trimming a batch of the same caliber cases can be quick. Note the setting adjustments for faster future setup

Below I have shown how to set up my favorite step by step.

Frankford Arsenal Platinum Series Case Trim & Prep Center

World's best case Trimmer, F.A.

This is the Platinum Series Case Trim and Prep Center. This is my favorite case trimmer and I dare say is the All in one case preparation unit. The trimmer is very accurate, has a spinning chamfer and deburr to clean the case mouth after trimming, and also includes a primer pocket cleaner. and these attachments can be changed with other store-bought attachments. Along with all that it also includes 6 washers (thin aluminum shiny disk) and 3 collets for high precision trimming. Any case from 0.17 Remington to 0.460 Weatherby can be trimmed using this baby. To store all these tiny washers and collets it has an inbuilt storage compartment. Do you like it too?

To set up the case trimmer,

  1. Open the trimmer head and find the washer that sits on the shoulder and the collet that has the best fit for your ammo case.
  2. Place them, first the washer then collet, and screw the head back.
  3. Then place your case in the collet and screw the head until there is no side-to-side wiggle and the case can be easily remover and inserted into the collet.
  4. To adjust the length, place the case in the collet, making sure the case mouth is just kissing the blade.
  5. Then measure your case and find out how much it needs trimming. Spin the dial to get the desired length.
  6. Give it a trial trim to check if further adjustment is required, go ahead and spin the dial.

Once the desired length is achieved, remove that case and insert the next case for successive trimming. It does not end there, after trimming use the chamfer, deburr, and primer pocket cleaner to completely prepare the case for reloading. Preparing one case takes me about 15-20 seconds. All the attachments are standardized, and if any components need changing you can readily change them with other standard brand components. As the name of the unit, it is a total “Case Trim and Prep Center” for your brass ammo case.

If you would like to evaluate your brass case trimmer or upgrade your equipment, you could consider reading the 10 Factors to consider when choosing a case trimmer to understand how we evaluate the case trimmers.


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