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Case Trimming

Necessary? Yes. Fun? Not really...
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High RPMs, like those provided by this old Dewalt drill, cut case mouths very quickly and cleanly when used with the World’s Finest Trimmer (WFT).

While a few handloaders actually like trimming rifle cases, they tend to use the loading room as a refuge from real life. Most well-adjusted handloaders regard trimming more than 50 cases on a typical hand-cranked tool as prison labor — something we’re forced to do if we want to shoot a lot.

We need to trim cases because the firing and resizing cycle stretches them, and the case mouths eventually run into the front of the chamber. This essentially crimps the case mouth slightly around the bullet, restricting its release as the powder starts to burn and raising pressures. This might not reach dangerous levels, but pressures jumping up and down from round to round don’t help accuracy.

We can put off trimming for a while by neck-sizing cases being fired in the same rifle. Since the neck-sized case fits the chamber closer, it can’t stretch as much during firing, and also doesn’t stretch by being forced into a full-length sizing die, squeezing the entire case body. The squeezed brass has to go somewhere, and since the shell-holder prevents brass from going “backward,” moves upward, into the neck-portion of the die.

However, neck-sizing normally works only for the rifle the cases are fired in. Chambers vary slightly in size, so neck-sized rounds tend to fit either very tightly in other rifles (if they fit at all) or they stretch even more.

Sticking to cartridges with relatively steep shoulder angles can reduce case-stretch when full-length sized just enough so there’s slight resistance when chambering a round. The sharper shoulder prevents the firing pin from driving the case further into the chamber, resulting in less stretch during firing. A shoulder angle around 30 degrees really helps, and more is better, the reason some high-volume varmint shooters prefer the .223 Remington Ackley Improved to the standard version. The 40-degree “Ackley angle” can prevent case-stretching for numerous firings.

Really thin brass like the .22 Hornet requires chamfering. This Gracey tool chamfers as it trims.

If You Must Trim, Do It Quickly

Unfortunately, many handloaders prefer older cartridges with more sloping shoulders (perhaps because many shooters are older with more sloping shoulders). These rounds tend to stretch no matter how little we resize them. The standard trimming method involves putting the cases in a manual lathe-type trimmer and cranking away.

This method has three major flaws. First, blisters often form on your cranking fingers. Second, inserting the case into the shell-holder means taking it back out again, both requiring considerable time. Third, the slow cutting creates burrs both inside and outside the case mouth, requiring chamfering (yet another form of forced labor).

Many lathe trimmers can be fitted with a drill motor, not only preventing blisters but potentially increasing RPMs, preventing the dreaded burrs from forming around the case mouth. But the best of all worlds is case trimming without the lathe.

Instead of inserting the head of a case into a shell-holder or collet, then pushing a cutter into the case mouth, the neck and shoulder are inserted into a steel mirror-image of itself, where a rapidly-spinning blade trims the neck in a couple seconds. We then pull the case out and insert another, a much quicker process.

I own several power trimmers, one a lathe-type used for small batches. But when trimming more than 50 cases, I use one of several “front end” trimmers because even with a motor-powered lathe, trimming and chamfering more than 5 to 6 cases a minute is impossible. With an insertion trimmer 20 cases a minute is pretty easy, so I can trim the 1,000 empty cases for an upcoming prairie dog shoot in an hour.

The Black Widow Trim-It II uses a chamfering cutter (visible inside the tool). Like the WFT, it can be mounted in a drill motor.

Bypassing Chamfering

Many high-volume shooters use boattailed bullets. For these, the case mouth doesn’t need to be chamfered, because if simply burr-free, the tapered bullet bases still seat easily. For some of these rounds the simple, the relatively inexpensive WFT (World’s Finest Trimmer) works great. I mount it in my ancient but powerful Dewalt drill, resulting in sufficient RPMs to trim .204 Ruger and .223 Remington brass burr-free.

Unfortunately, among my other favorite high-volume varmint rounds are the .17 and .22 Hornets, with necks so thin they’ll collapse if the bullet hangs up at all. Here my Gracey bench-mounted trimmer gets the job because its cutter chamfers while it trims, both inside and outside the case mouth. The Gracey includes its own high-RPM motor with interchangeable “shell holders.”
For handloaders who load lots of rounds in only one or two cartridges, the Black Widow Trim-It II also features an easily adjustable chamfering cutter. Like the WFT, it fits in a drill motor and costs a lot less than bench-mounted trimmers like the Gracey.

Shakespeare’s Macbeth once said (although on a different matter), ”If it were done when ’tis done, then ’twere well it were done quickly.”

This definitely applies to case trimming. Luckily, practical electric motors appeared in the mid-1800s. So if you want to trim a lot of cases and still have a social life, electricity’s the answer.

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