Reloading: Trimming Cartridge Cases

OK, so maybe this isn't the most precise way to trim your cartridge cases...

OK, so maybe this isn’t the most precise way to trim your cartridge cases…

SERIES

Part 1: Want to Reload Your Own Ammo? Basic Questions to Consider

Part 2: The Reloading Process
Part 3: The Gear You’ll Need and What It’ll Cost You

Part 4: Brass Cleaning and Preparation to Load

Part 5: Brass Resizing

Part 6: Trimming Cartridge Cases

Part 7: Repriming the Cartridge Case

Part 8: Powder, Propellants, and Pressure

Part 9: All About Primers

Part 10: Projectiles: Materials, Weights, and Styles

Part 11: Seating and Crimping Bullets

Part 12: To Crimp or not to Crimp

Part 13: Final Inspection and Packaging Tips

While touring the FN factory last week, I got an up close and personal look at their process for cold hammer forging barrels. In case you don’t know how that works, they stuff a steel rod, with an oversize hole for a bore, into a machine that hammers the living snot out of the barrel blank. A mandrel inside has the mirror image relief cut of the desired rifling pattern. As the hammers mash the steel into the mandrel, the bore takes the desired shape. It’s kind of like doing auto repair with a hammer – just pound away ’til all is right.

Why do I mention this in an article about cartridge case trimming? Because those steel rod barrel blanks stretch several inches during the process of taking such a drubbing. A similar thing happens when you resize rifle brass, although the process isn’t quite as dramatic. When you stuff the cartridge case into a resizing die, it’s subject to pretty intense pressure from the outside in. That pressure reforms (basically crushes) the brass back into its original size and shape. During this process, the brass stretches in the direction of the case mouth. Ipso facto ergo e. Pluribus Unum, after one or more resizings, depending on the brass type, caliber, and load, the cartridge case is a little longer than it’s supposed to be.

Before you begin the process of adding new propellant and seating and crimping a new projectile into place, you need to trim that case back to its “trim to” length. If you don’t, you’ll get all sorts of wonky results when trying to crimp. Or maybe your newly completed cartridge won’t fit into the chamber. Or worse yet, you might end up pressure variances that impact accuracy depending on how long the case is compared to spec. For all these reasons, you’ve got to inspect the length of your bottleneck rifle (but sometimes pistol) cases and if necessary, trim them back to the proper length.

To find the proper “trim to” length, just check your reloading manual. It’ll have that exact number so you can cut with confidence.

There are a number of ways to do this, and like most things in reloading, your choice of which one largely depends on your anticipated volume of work, your need for precision, and your patience level. In other words, you can spend more money on equipment and get more automation (and more production per hour) or you can do things by hand at a slower pace, but spend a lot less money on case trimming gear.

Depending on the type of trimmer you choose, you might also need a separate tool to chamfer and deburr the case mouths. The trimming operation leaves a rough, flat cut. Chamfering applies a slight bevel to the inside of the case mouth to bullets seat smoothly and evenly. Deburring takes the rough edges off the outside of the case and usually applies a bevel there too.

This Lyman hand tool chamfers and deburrs with a different tool head on each end.

This Lyman hand tool chamfers and deburrs with a different tool head on each end.

The Hornady Lock-N-Load Case Prep Trio motorizes the chamfer and deburr process among other functions.

The Hornady Lock-N-Load Case Prep Trio motorizes the chamfer and deburr process among other functions.

 

One more thing before we get into trimmer types. A case gauge  is an indispensable tool, especially for bottleneck rifle cartridges. This gauge replicates the inside of a chamber for a specific caliber. Simply by dropping your cartridge case into the gauge you can tell if the case is resized properly and if the head space is correct to spec. It’s the best way to make sure your resizing die is set correctly. It’s also a super quick way to tell if your cases need trimming. Since you’re looking by eye, you won’t have 1/1,000th of an inch precision, but you can easily spot cases that are excessively long or short. If you really want to see what’s going on with your cases, invest in Sheridan Slotted Case Gauges. They’re significantly more expensive, but give you a view of exactly how your cartridge cases conform to a perfectly sized chamber.

Dropping your case into a gauge will tell you that resizing and headspace are correct.

Dropping your case into a gauge will tell you that resizing and headspace are correct.

You can also see at a glance if your case is too long.

You can also see at a glance if your case is too long.

Let’s look at a few approaches with an example of each. I’ll try to roughly order these case trimming options from least expensive and lowest production rate to pricier but faster.

Hand Trimmers

It’s hard to go wrong with a classic hand-operated case trimmer like the Forster Original Case Trimmer. These are miniature lathes. One end holds the cartridge case while the other has a blade that turns via a handle to trim the case mouth. Specifics vary by manufacturer, so check to see if your model of choice (like the Forster) requires specific size collets and guides for the case base and mouth respectively.

This Forster Case Trimmer is simple, affordable, and precise.

This Forster Case Trimmer is simple, affordable, and precise.

While the trim rate is limited by how fast you turn, precision is excellent with a quality model like the Forster. Without a 75 horsepower motor, you have excellent control over even the lightest trim settings. Many models have an optional adapter to add a motor or power drill so you can ditch the hand cranking.

Most hand trimmers execute a flat cut, so you’ll need to chamfer and deburr separately. The Forster Original runs right about $100 and comes with a variety of collets and pilot guides. Other brands run a bit less depending.

Little Crow WFT Trimmers

Another nifty invention is the Little Crow Gunworks World’s Finest Trimmer. That’s WFT, not WTF! This clever device mounts in a standard hand drill or drill press. Instead of mounting the cartridge case in a lathe for trimming, you simply press a case into the unit while it’s spinning. The outer body sets length by stopping the case shoulder at a point you adjust. Each case takes seconds to trim so you can move through a pile pretty quickly. Between pressure and vibration, your fingers will get a workout, which might be a good thing if you’re learning to play the banjo.

The Little Crow WFT attaches to a power drill. Just insert the case like this to trim.

The Little Crow WFT attaches to a power drill. Just insert the case like this to trim.

The original WFT was caliber specific, so you had to order one for each caliber you trim. The new WFT 2 model has caliber inserts so you keep the main body and swap inserts to change calibers. You’ll need to chamfer and deburr separately with this approach also.

 

Feel free to go full redneck and set up something like this for hands free operation of the drill. Note the zip tie on the trigger. That's probably not OSHA approved...

Feel free to go full redneck and set up something like this for hands free operation of the drill. Note the zip tie on the trigger. That’s probably not OSHA approved…

The original Little Crow WFT (caliber specific) is $72 at Brownells while the new WFT 2 runs $72 plus $27 for each caliber-specific trim chamber insert.

Trim-It II

Like the WFT 2, the Trim-It II uses a standard drill, a drill press, or their own standalone motor to drive the trimming unit. Caliber inserts allow the same body to handle most any rifle or pistol caliber. In that respect, it’s kind of similar to the Little Crow WFT.

Here’s the big difference. The Trim-It II uses a special carbide blade that cuts and also creates a 15-degree chamfer inside the case mouth and a 45-degree bevel and deburr on the outside – all in one pass. After initial length and chamfer adjustment, just press a case into the unit and everything is done in one step – no need for a separate chamfer and deburr tool.

The Trim-It II runs $132.50 direct plus $19.95 for each caliber conversion die.

Dedicated Bench Trimmers

I’ve been using an RCBS Trim-Pro Power Case Trimmer for years. This is a motorized unit that mounts to your bench. I mounted mine to a sturdy piece of wood so I can clamp it to most any surface where I want to work. Oh, a quick note from my experience. Doing this in the kitchen is often frowned upon as the process generates lots of little brass shavings. Apparently those gets in the pheasant under glass and make it crunchy.

case-trimming

The RCBS Trim-Pro Power Case Trimmer is great for volume and large cases.

The trimming process is pretty fast. The Trim-Pro has shell plates at one end. Press a cam lever down, drop a cartridge case in the shell plate, then release the hounds. Actually, a spring loaded mechanism allows the motor to move towards the stationary shell holder. Course and fine adjustment rings allow you to set the exact amount of travel for the motor, and this establishes your case length. As the unit has a positive stop, there’s no risk of over trimming, just insert the shell, release the motor, and let it run. The motor even shuts on and off as the trimmer engages. You’ll appreciate this type of approach over a hand lathe or drill model if you’re working cases with thicker brass – the machine does all the work. It’s easy on the fingers and no hand cranking.

If you go this route, splurge on the optional 3-way cutter head. Like the Trim-It II, this blade cuts, chamfers, bevels and deburrs all in one pass. If you’ve got lots of big brass cases, this approach may be well worth the money. The Trim-Pro costs about $310 at Brownells.

Press Trimmers

When you’re ready to get cookin’ with gas, consider a Dillon RT1500 Case Trimmer. This unit mounts to virtually any single-stage or progressive reloading press in a standard die position. The best part is that the resizing die is integrated with the trimmer, so the case is cut to the right length in the same press stroke as the resizing operation. It saves a whole step in the case preparation process.

The other best part is that the ¼ horsepower motor eats brass like Rosie O’Donnell eats Pop-Tarts, so you can even do things like a one-pass conversion from .223 Remington to 300 AAC Blackout cases. The .223 case is trimmed and shaped as you go – all in a couple of seconds. The unit has a vacuum tube port so you can hook a small shop vac up to catch all the brass shavings while you stock up on sized and trimmed cases. Combine this with a progressive press and case feeder and you’ll be resizing and trimming brass by the thousands in no time. The only drawback to all this brass destruction glory is that the unit does not also chamfer and deburr.

It’ll cost ya about $330 plus the Rapid Trim dies you need for your calibers.

And there you have it. Like most other steps in reloading, you have a choice as to how much automation you want to buy. You can start small, and relatively inexpensively with a hand-operated lathe trimmer like the Forster, and it will take you a long way. In fact, much like a single stage reloading press, you’ll find that you’ll use the hand trimmer forever. They’re easy to adjust and perfect for small batches when it’s not worth the time and trouble to reconfigure a fancy power trimmer.

Next up, powder and primers! Boom!

{ 4 comments… add one }
  • Boba Fett June 5, 2017, 6:28 am

    Tom,

    I know this is an old article, and I’m not sure if your respond to comments, but… Is it a problem if the mouth of your trimmed cases aren’t perfectly level? My trimmer is slightly askew, so when I go to check overall case length after trimming, one side of the mouth is maybe one or two thousandths higher than the other. Will that effect accuracy?

  • Petercat April 13, 2016, 12:37 am

    No mention of the Lee case trimmer?
    $8.00 for the cutter, $6.00 for each caliber. I’ve been using them for years, never a problem.
    Chuck it into an electric drill or trim by hand.

  • DRAINO April 11, 2016, 3:57 pm

    I see a “case gauge” mentioned, but I don’t see a set of calipers listed. Maybe that was covered in a previous article, but in case not….YOU NEED IT! These can range in price, but I consider them a necessity. A decent set will last forever. But I love these articles…Good job! Keep’em coming.

    • Tom McHale April 12, 2016, 9:32 am

      Excellent point, thanks for adding this. I mentioned calipers in the “gear” article but forgot to explain here why they’re so important for case trimming too. Absolutely agree, calipers are a “must have” for this step!

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