Power case trimming

Power Case Trimming  (a chapter from Gun Gack II)

Enjoy this free chapter from Gun Gack II, on power case trimming.

Some shooters believe rifle brass stretches when the neck gets pulled over an expander ball, but experiments with the expander assembly removed have proven this isn’t so. Some shooters also believe brass flows forward during firing, like a glacier, but this doesn’t occur at normal pressures. Instead, handloaded rifle cases “grow” longer because they’re fired in chambers that, by necessity, are slightly larger than the case, then get resized to fit in the chamber again. When a fired case is full-length sized, the squeezed-down brass has to go somewhere, and since the case head is positioned firmly against the shell-holder, the only direction possible is forward.

Eventually cases lengthen enough to require trimming their mouths; otherwise the mouth gets crimped around the bullet by the front of the chamber, increasing pressures. Many handloaders hate case-trimming, especially handloaders who shoot a lot. My particular downfall is the abundant burrowing rodents living in the West, considered pests by farmers and ranchers because they gobble uncountable tons of valuable hay and pasture each year. Some landowners resort to poisoning, but many allow varmint hunters to maintain some sort of balance between rodents and crops.

In Montana we call both Columbian and Richardson’s ground squirrels “gophers.” It’s not uncommon to expend 500 rounds in a day of gopher shooting, and prairie dog shooting sometimes involves similar amounts of ammo. It’s no fun to trim hundreds of cases with a hand-cranked trimmer. I used to do it, back when I had more time than money, but soon learned to wear a glove on my cranking hand to prevent blisters—and still hated the job.

Most handloaders who shoot a lot have to trim a pile of cases, whether because we’re stubborn enough to continue shooting slope-shouldered rounds, or because after several firings we have to full-length size sharper-shouldered rounds so they’ll chamber again. For high-volume trimming, electric power really helps, saving time and bypassing blisters.

There are two basic kinds of power trimmers, those that “index” (control) case-length from the base of the case, and those that index from the shoulder of the case. Each has virtues for certain types of trimming.

Base-indexing trimmers include most of the common hand-powered trimmers such as the well-known Forster, Lyman and RCBS, where the case-head fits into a shell holder, and the trimmer blade is shoved against the case mouth and turned. As a result, base-indexing more precisely trims cases to an exact length than shoulder-indexing, and many base-indexing trimmers can also usually be used for outside neck-turning.

However, handloaders after super accuracy often use a separate hand-tool for turning necks, and the precision of a base-indexing tool depends on the system used to hold the base. The Forster and some others use a collet, which isn’t quite as precise as butting the case-head firmly against a metal wall, as in the RCBS Trim Pro. However, the Forster system has the advantage of being slightly quicker when switching cases, as does Lee Precision’s Quick Trim, which fits on a typical loading press and uses standard shell holders.

Many hand-cranked base-indexing trimmers can be powered with an electric drill (including the Lee), but I primarily use two, a hand-cranked Forster owned since the 1970s, and an RCBS Trim-Pro Power Case Trimmer acquired 20 years later. The present RCBS version is called the Trim-Pro 2, with a universal shell-holder, but mine’s the original, requiring different shell-holders for each case-head size. The universal holder can be purchased for around $50, but I’ve never bothered upgrading because of already owning quite a collection of shell holders.

My Trim-Pro is still working more than a quarter-century of hard use. However, as with many relatively complex power tools, occasionally small parts must be replaced, one reason I keep the Forster. It’s simple enough to have never required repair—and serves as a back-up on the rare occasions when the Trim-Pro is waiting for a part.

The downside of case-head indexing trimmers, no matter the design, is they’re comparatively slow. Many handloaders who’ve never used anything else except a hand-cranked trimmer don’t believe this, but it’s true. Each case must be inserted into the shell holder, the trimmer blade pushed against the case mouth and turned, then backed off, and the case removed from the shell holder. I’m pretty quick with my Trim-Pro, but the maximum output is around six cases per minute, so I primarily use it for big game or test ammunition, where I rarely trim more than 50 cases at a time.

Shoulder-indexing trimmers don’t trim quite as precisely, because even when cases are neck-sized, slight variations in brass thickness result in tiny differences in shoulder dimensions. But except for super-accuracy shooting, where every cartridge should be as exactly the same as possible, a slight difference in head-to-shoulder length doesn’t make any difference.

Shoulder-indexing tools are much faster, because the base of each case doesn’t need to be fitted into a shell holder. Instead the case is inserted neck-first into what most companies call (for some reason) a “case holder,” essentially a short chamber dimensioned to fit the neck and shoulder area of the case. The spinning cutter sits just beyond the case holder, so the case mouth is immediately trimmed upon insertion. All we have to do is push a case in, hold it for a second or so, then pull it out. As a result, a really motivated and organized handloader can trim at least 20 cases a minute. Even when taking short breaks, for whatever reason, this allows trimming around 1000 cases an hour.

Shoulder-indexing trimmers can be very simple and inexpensive. Some are merely a case holder and cutter, on a shaft designed for insertion in an electric drill. The one I’ve used most extensively is the WFT—short for World’s Finest Trimmer—designed by Dale Hegstrom of Little Crow Gun Works in Minnesota.

I’ve been using WFTs since they appeared, one for rounds based on the .223 Remington case with the standard shoulder angle of 23 degrees, and one for .223-based cases with 30-degree shoulders. The cutter depth can easily be adjusted for short cases from the .221 Fireball and .300 Blackout up to the .17 Remington and .204 Ruger—and the case holders can also be easily switched, though I prefer having two WFTs set up and ready to go. Hegstrom continually expands and improves the WFTs, and today makes versions for cases up to the .50 BMG.

Here we should discuss case-mouth chamfering. If we have to chamfer each case after trimming cases, then we’ve lost much of the speed advantage in power trimming, but there are at least three ways to chamfer while trimming.

With the WFT, running the drill at higher speeds results in a very smooth cut, without a burr forming inside and outside the case mouth, as it normally does with hand-cranked trimmers, or even slow-turning power trimmers. This is why I use an old, made-in-USA DeWalt half-inch drill, with an actual cord that plugs into a wall socket: The RPMs can be cranked right up there, and stay there without having to recharge the drill. Turning the case slowly in the direction of the cut during trimming (the technique suggested in the WFT instructions) results in a case mouth without burrs. Since I load boattailed bullets in most varmint loads from .20 caliber up (apparently there aren’t any boattailed .17 bullets), the mouths don’t require any chamfering, but many square-base bullets also load with no problems.


ammunition case trimming

My old American-made DeWalt half inch drill at work.


Some power trimmers use a chamfering tool to perform the trimming. I’ve used several of these, but eventually decided to avoid any requiring more than the simplest adjustments, because adjusting took too much time, and power-trimming is all about saving time. One example is the 3-Way Cutter available for the RCBS Trim-Pro, which works well but requires adjusting two cutters, one for chamfering inside the case mouth and one for outside. Both must be adjusted every time you trim cases of a different caliber, but since the Trim-Pro’s relatively slow motor takes a few seconds to slice off excess brass, I eventually decided to chamfer a just-trimmed case with a hand tool while the Trim-Pro grinds away on another case.

These days I use Little Crow Gunworks’ Precision Prep Tool, a nifty hand-held design with a spinning turret-head mounted on ball bearings. It holds up to four tools, which really speeds up chamfering compared to a typical hand-held tool that must be flipped 180 degrees to switch from inside to outside chamfering. However, if you mostly trim one caliber the RCBS 3-Way Cutter would probably save time, since it could be adjusted and left alone, ready to go.


bullet case trimming

The Little Crow Gun Works’ Precision Prep Tool


The Gracey Power Case Trimmer, a bench-mounted shoulder-indexing tool, also uses a chamfering tool requiring adjustments of both the inside and outside cutters. They’re even more of a pain to adjust because adjusting each cutter also changes the overall case length. Luckily, the Giraud Power Trimmer uses a single chamfering blade with a V-notch, requiring minimal adjustment—and fits the Gracey tool.

Years ago I came across a lightly used Gracey for an excellent price, complete with the factory motor and a dozen case holders, and use it with a Giraud chamfering blade for power trimming some cases. Even when new, the Gracey costs over $100 less than the Giraud—but the Giraud’s motor is more powerful, and extra case holders cost a few bucks less. Both are excellent units that can quickly trim and chamfer hundreds of cases.


ammo case trimming

The Gracey bench-mounted trimmer


Recently I tested the Black Widow Trim-It II, a simpler power trimmer that, like the WFT, can be mounted in a drill, but like the Giraud uses an easily adjusted V-blade chamfering cutter. Case-length can also be precisely adjusted with a micrometer collar. It also works really well on my DeWalt drill, and the price is $132.50, with extra case holders $19.95. The Trim-It came with a case holder for the .308 Winchester, another cartridge I shoot a lot, and I adjusted the tool to trim cases .01 inch shorter than maximum—a common trick to reduce the need for trimming each time a case is fired and resized.


bullet case trimming tool

The Black Widow Trim-It II


Most shoulder-indexing power trimmers use case holders designed for full-length sized brass, so neck-sized brass often won’t fit. However, Little Crow Gun Works will modify a shell holder for neck-sized brass, free of charge, if you send in a few sample cases, and custom case holders are available at reasonable prices for all the shoulder-indexing trimmers mentioned. No matter what your needs and budget, there’s a power tool out there for every handloader who shoots a lot—and hates case trimming.

Want to learn more? Get your copy of Gun Gack II here.

1 reply
  1. Larry Munn
    Larry Munn says:

    John, Your advice on case preparation and sorting cases for neck uniformity has helped me with accuracy much more than years of moving 0.1 or 0.2 grains up and down on powder charges. Thank you.
    Eileen, Last night coming up on dinner, we had no chips in the house (??) so I cut wedge shaped slices of your Irish brown bread from the Wild Bowl and we dipped it in a plate of olive oil and balsamic vinegar. The guests (and my wife) loved it and were amazed that I had actually baked it while they were out in the horse barn. Thank you.


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