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How to Trim Brass

When a cartridge is fired from a rifle on a game reserve or firing range, the cases often are reclaimed, reconstructed and reloaded to be used again. However, the trauma of the initial shot pinches and stretches the case. This often renders the case too long for use with the original firearm. In these cases, a process known as trimming the brass is employed in which the case is shortened to make it usable again. Trimming must be done on an empty shell case; trimming a loaded shell cartridge is dangerous. Brass trimming is relatively simple but requires some expensive specialist equipment, such as a pillar drill and a trimmer press.

Things You'll Need

Ruler
Maximum cartridge length chart
Screwdriver
Plywood
Drill trimmer bit and base unit
Pillar drill

Instructions

- 1
  Measure your cases in inches. Check the case length chart next to the make and model of your firearm. There will be a maximum length and a trim-to length. If your case length is more than the maximum length, you will need to trim it to below the maximum length. The trim-to length is the recommended length for trimming. Gun club magazines and websites provide these charts.
- 2
  Screw the screws around the base of the trimmer press into a piece of plywood to keep the press secure. Place the rim of the case into the trimmer press so that the tapered end is facing upward. Move the lever on the press so that the two flanges grip the rim of the case. Twist the press clockwise and the case will lock in place.
- 3
  Open the box of trimmer buttons inside the trimmer case. Remove the button that matches the caliber of the case and attach it to the cutting end of the trimmer bit. Place the other end of the bit in the mouth of the chuck and turn the lever to lock it in place. Place the plywood with the trimmer press below the drill unit and pull the lever to bring the drill down. Check that the trimmer bit and the top of the case line up; use a G-clamp to clamp the plywood to the work table.
- 4
  Bring the safety guard down and turn on the pillar drill. Slowly bring the drill down till the trimmer bit touches the top of the case and trims it slightly. Trim a little bit each time, then measure the case length. Remember that you can always trim more but you cannot trim less. When the length is below the maximum case length, your job is done.

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