You loaded a batch of 9mm last night. This morning you drop the first round in your case gauge. It stops partway down and sits there. Now what?
How Case Gauges Work
The RCBS Chamber/Case Length Gauge is about as simple as a tool gets. This go/no-go style tool works by dropping a loaded round into the precision-made gauge. If your ammo fits the gauge, it will fit your pistol. The gauge checks both chambering and cartridge length, so you can check case length, diameter, and overall cartridge length in one drop. The design is one piece and non-adjustable.
If you have a reloaded round that doesn't fit into your gauge, something is off about a key dimension of your ammunition. So why would your pistol ammo not fit in the case gauge?
Four Common Causes
Too Much Crimp
Like most semi-automatic pistol ammunition, a 9mm Luger round requires a taper crimp. Put simply, a taper crimp squeezes the case around the bullet, usually done in one step during the bullet seating process. Done right, the crimp leaves no indentation or other visible sign of a crimp, and it takes the bell out of the case mouth that you put in during the expansion step before seating the bullet.
Push harder and overcrimp, and you can cause issues with your ammo. Excessive taper crimp can produce pressure that causes bulging that prevents chambering. Overcrimping bulges the case neck and causes you to lose neck tension on your bullet as well. That bulge is what your gauge caught if your round is too fat to fit inside.
To make sure your reloads are in spec, measure your taper crimp with a pair of calipers. Post crimp, the case mouth should measure .001" to .002" smaller in diameter than before. Another check is using your hands on a test round to move the bullet. If you can't pull the bullet in or out but you can twist it side to side, you're likely putting too much crimp on your round.
The Wrong Crimp
Some pistol die sets are sold with either a roll crimp or a taper crimp as an option. A roll crimp is typically only required for heavy-recoiling magnum loads and is overkill for a cartridge like 9mm. This is why RCBS only offers a taper crimp option for 9mm, but offers both a roll crimp and a taper crimp die option for .357 Magnum.
Too Much Expansion
You flare the case mouth, also called expanding or belling, after resizing your pistol brass so that the bullet seats appropriately and does not shave its jacket on the way in. It's easy to go too far. Flare to bullet diameter plus .030" or less. Excess flare makes bullet seating, crimping, and the eventual feeding, function, and firing of your round harder or impossible.
The Sizer Die
Without correctly resizing your case back to proper dimensions, it may not fit back into your firearm's chamber or into your case gauge. One reason someone may not be correctly resizing pistol brass is the setup of their carbide resizing die. Carbide sizing dies do not require the cam over process we recommend for rifle dies. Instead, set up your pistol die by stopping when the die touches the shell holder, or leave a small 1/16" gap. Cam a carbide die over and you risk hurting the polished carbide ring insert inside the die body, and potentially your sizing along with it.
| What to Check | Where It Should Land |
|---|---|
| Taper crimp | Case mouth .001" to .002" smaller after crimping than before |
| Case mouth flare | Bullet diameter plus .030" or less |
| Carbide sizer die | Contact with the shell holder, or a 1/16" gap. No cam over. |
Length Is Rarely It
Straight-wall pistol brass doesn't grow much, and rarely if ever needs to be trimmed. Case growth after firing and resizing is generally small enough that the cases can be left alone.
Check your case length anyway against SAAMI standards in your reloading manual, because it's quick. As with resized rifle brass or any other kind, cases that run out of spec long may stop your round from chambering and can even create problematic pressure.
Your Pistol Gets the Last Word
Your case gauge is a great way to keep your reloads in spec and at top quality. That said, a gauge is a check, and it may be different than your chamber.
Chambers differ, so pull your barrel and drop a few dummy rounds in before you load two hundred more. Your pistol gets the last word.
Check it before you load 200 more
Chamber gauges, carbide pistol die sets, and calipers, all in stock.
Always follow safe reloading practices. Consult current published load data and your equipment's instruction manuals before beginning any reloading operation.
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