RT1500 Electric Case Trimmer

Trimming Brass
By John Bibby

One of the components of reloading is the cartridge case, or “brass.” Unlike some of the other components used in reloading, brass needs to be prepped. This is especially true of previously fired brass.

The process of firing a round of ammunition creates intense pressure. In addition to sending the bullet down the barrel and towards the target, it also places expansion stress on the brass. How the brass handles this stress depends on several factors. The first of these is the peak pressure of the cartridge. The second is the design of the brass itself. The third is how well the unfired brass matches the chamber.

Peak pressure:

This is the maximum amount of pressure between ignition and the bullet exiting the barrel of the gun. This is the pressure level that affects the brass the most.

Brass design:

In a bottleneck cartridge – think 5.56, .243 or .308 Win. The pressure hits a funnel, which compounds the pressure wave in the neck area. It also has a tendency to push the brass expansion out towards the barrel. This happens more with some designs and less with others, but it is always a concern with bottleneck brass. It is much more of a concern with higher-pressure loads or cases with less angled shoulders. A case with high pressure and 20-degree shoulder angles will have more growth of the neck than a case with either lower pressure or 40-degree shoulders. In either case, a quick check of case length after resizing it will determine if it is beyond maximum length.

If the brass is too long, using a manual trimming die or power trimmer will get them back to an appropriate length. Failure to do so can cause neck separation, serious over-pressure issues or sometimes both.

In a straight-wall cartridge – think .45 ACP, .38 Special or .444 Marlin – the pressure does not hit a funnel. It simply pushes the bullet towards the barrel and the brass towards the chamber sides. This causes the case to form to the chamber but does not cause much (if any) stretch in the length of the case.

It is rare to ever need to trim straight-wall ammo. That does not mean pistol ammo does not need to be trimmed. There are many bottleneck pistol rounds, .357 Sig comes to mind.

Chamber fit:

In most modern firearms, this is not a large issue. It is more of an issue for precision reloaders. They will often fire cases and only neck resize. This greatly reduces both the work stress on the brass and the amount of brass growth caused by resizing. Chamber fit also becomes much more important with regards to wildcat cartridges and fire forming.

In cases that need trimming, it is rare to need to cut them down more often than every three firings. If you are, it is usually an indication of too hot of a load, too soft or poor quality brass. It is also important to trim to the trim length, which is significantly shorter than the maximum length. Doing this decreases the frequency of trimming and helps to gauge how much the case is growing with each firing.

In precision reloading, shooters will often full-length resize new brass, then trim each case to the same length. This is one step towards insuring case uniformity. Most people do not do bother with this step unless they are chasing very small group size.
In stock
The RT1500 Electric Case Trimmer is designed to handle the heaviest trimming jobs, including converting 223 Remington into 300 AAC Blackout. The RT1500 makes short work out of trimming large quantities of brass.
The RT 1500 trim die is used just like a standard size die. The big difference is that while you are pushing the case into the die to size it, a 1/4 horsepower electric motor driving a carbide cutter is trimming the case to length. Chips are drawn off through a vacuum manifold that clamps to the outside of the special size/trim die. (Vacuum cleaner and hose not included.) Outside diameter of manifold is 1.250" where the vacuum hose connects.
The RT1500 is equipped with a quick-disconnect power cord; and it can be used on any standard reloader, single stage or progressive. See below for caliber exceptions.

Available only in 110 volt /60 Hz.
NOTE: Toolhead and Size/trim dies are sold separately. Case lube must be used to size and trim brass.

Replacement Carbide Cutting Blades, stock#13141

All the electrical/electronic components of Dillon equipment are covered by a one-year warranty from date of purchase.

In order to trim 300 AAC Blackout or 6.8 SPC, you must be aware of the following:

    WARNING: This product can expose you to chemicals including lead, which are known to the State of California to cause cancer and reproductive harm. For more information, go to https://www.P65Warnings.ca.gov

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