If I had to point to one reloading accessory inexperienced handloaders sneer at, and say, “I don’t see WHY I need one of those,” but experienced handloaders understand is absolutely invaluable, it would be the case gage. (Why it’s spelled “gage” instead of “gauge” is beyond me, it just is.) A case gage is a cylinder-shaped piece of stainless steel that’s had drilled into it, longitudinally, a hole equivalent to a very tight match chamber for a particular cartridge. After handloading, you use the case gage to check a cartridge’s external physical dimensions. If it’ll fit into the case gage, it’ll fit into a gun’s chamber.
One primary thing a case gage can catch, before that cartridge makes its way into your gun and stops it working, is the slight “pregnant” swelling of an autopistol casing that was right over the unsupported area of the feed ramp during firing. Standard sizing dies only resize about the top 2/3 of a casing, because we don’t want to be working the bottom 1/3, i.e. the area where the web meets the interior case wall; that can stress the brass so much, in a critical area, we could wind up with a case head separation during firing.
As anyone who’s ever experienced one can tell you, case head separations suck, because you wind up with a circular piece of brass fire-formed to the interior of your gun’s chamber that’s quite difficult to get out. This is a procedure requiring time, and tools. Ask me how I know.
So, since dies only resize the top 2/3 of casings, it’s quite possible to load ammo that has the un-resized bottom of the casing still so “pregnant” it won’t fit into the chamber, leading to a failure to feed during live fire.
This phenomenon has, historically, been so associated with casings fired in Glocks you’ll actually hear it called “Glock bulge.” The myth is that Glocks have “unsupported chambers” to assist in feed reliability. While there may be some truth to this in .40 S&W, it’s absolutely untrue in 9mm. Honestly, I think this idea has a lot more to do with 9mm Glocks’ popularity than their chambers being particularly, in the overall scheme of things, unsupported. 9mm Glocks actually have fairly tight chambers. You want to talk guns that have absolutely HUGE chambers: the SIG P220-series in 9mm. You can always tell when you’ve picked up 9mm brass that was fired in a SIG P225/P226/P228/P229, because it requires WAY more effort on the handle to resize, and “pregnant” rounds, even after all that work on the handle, are quite common.
While some people will say, “You don’t need a case gage, just pull the barrel out of your gun and use its chamber to check ammo,” the truth is it’s a lot easier, and probably cleaner, to use this little piece of stainless steel than having to pull a dirty, oily barrel out of a gun and use it, then reassemble the gun afterward, every time you want to check your handloads.
When you drop a round into the case gage, this gives you a golden opportunity to check the primer. To start with, you can make sure there’s actually a primer there. I don’t care who you are, and how experienced, the bottom line is we all, occasionally, put together a round without a primer. This is a bad thing, and the case gage allows you to catch that before your gun goes click instead of bang.
Also, you can catch those occasional instances where you’ve accidentally loaded a primer into the primer tube upside-down. When you drop a round into the case gage then visually check it, you see a trefoil-shaped anvil staring at you instead of a smooth primer cup.
Finally, primer-wise, take this opportunity to make sure it’s been fully seated. If it hasn’t, when the firing pin hits the primer, the fact it doesn’t have its anvil hard up against the bottom of the primer pocket, instead there’s a gap between the two, means the firing pin will actually push
the primer forward when it hits it. This absorbs enough impact energy that you can have a failure to fire. After dropping the round into the case gage, take a moment to run a finger over the primer, you want to feel it seated actually a bit below the surrounding brass.
You need to understand, in 9mm, there’s such a huge variance in the width of case rims, frequently you’ll have a round fail to seat fully in the gage, not because there’s anything wrong with the overall external dimensions of the case body per se but simply because the rim is too wide. This doesn’t mean the round has failed the gage. When a loaded round of 9mm goes easily into the gage, but the rim is still butted up against the top of the gage and not entering the hole, that’s still a good round.
The final thing a gage can catch for you is split casings. Fire a casing enough times, expand it through pressure, then work the brass by sizing it back down, eventually it’s going to weaken enough it splits longitudinally when seating a bullet during the reloading process. This results in an oversized “fat” cartridge that won’t fit into the chamber, leading to a failure to feed during live fire. When inserting a round with a split casing into a case gage, a very distinctive sort of tactile feedback, and a very distinctive sound, occurs. You can feel it, and you can hear it. The results are kind of hard to describe, but I would say it both feels and sounds “crunchy.” Once you’ve known it, you’ll never mistake it for anything else.
You can always tell the inexperienced versus the experienced handloader. The former is the person constantly shucking oversized rounds out of their gun during a match or practice session, as they experience feedway stoppage after feedway stoppage because many of their rounds won’t fit into the gun’s chamber. These are the people who’ll say to you, “I don’t see WHY I’d need a case gage.” Experienced handloaders are the people to whom that never happens, their guns just run flawlessly, because they own a case gage for every cartridge they load.
