A Case for the Gauge

In terms of equipment, a solid match performance rests in large part on match quality ammunition. Regardless of whether you reload, one of the most important quality inspection tools that you can use to insure that you’ve got match ready ammo happens to be a simple piece of steel that’s had a chamber reamer for your caliber of choice run into it the proper depth. They call it a “case gauge”.

There’s really not much to say about the case gauge, honestly. It’s operation is very simple – you take your ammo of choice (reloads or factory), drop them into the gauge one by one, insure that they go in all the way, and dump them back out into a different container. You can even do this by feel after very little practice. A round that’s good to go will drop freely into and out of the gauge (this is also called “drop checking” the ammo). The rear of the case head will be flush or below the face of the case gauge (so, if you feel the case head sticking up above the face at all, you have a potential issue). You can rest the gauge on a table – this will also catch rounds that are too long according to the SAAMI spec for the cartridge. Finally, you can also run your finger over the case head to check for high primers (the primer should be noticeably below flush with the case head for proper ignition).

In the past, I’d just used my barrel. What’s better than my actual chamber, right? A case gauge, that’s what. The thing is, the barrel has a cut in it for the ramp and/or throat that allows the gun to actually feed ammunition in from the magazine. That cut is primarily what leads to one of the biggest problems we’re looking for with the gauge in the first place – bulge. Depending on how your barrel is cut, there’s a 25-35% chance that a bulged round might chamber (and therefore drop check ok). That same round could cause a major issue when you then try to feed that same round into the chamber later, when it’s almost certainly going to be in a different orientation. You know who Mr. Murphy is, I’m sure… he’s going to make sure that every bulged round will drop check fine, and then be oriented to cause maximal distress once you get to the big match!

A second benefit to a case gauge relates to how they’re made. Typically, they’re cut to be at the minimum SAAMI spec. Your chamber, on the other hand, is almost certainly not that tight for reliability reasons. That means that the gauge is going to be more likely to reject rounds than the barrel, which just contributes to reliability. The gauge also doesn’t change due to the firing cycle, and therefore highlights any changes in your ammo quality more easily.

If you’re using a tapered case, like the series of cases based on 9×19 (9×21, 9×23, et al), drop checking your ammo in a case gauge becomes even more important, as case bulges with a tapered case can cause severe death jams when the bulged case wedges itself tightly into the chamber.

You’ll notice I mentioned drop checking factory ammo, too. I’ve actually seen more problems related to overly long cases and that sort of thing with factory ammo than I’ve seen with reloaded ammo. Brand new factory ammo typically won’t have a bulge in it – that would be highly unusual. But, it’s not unusual for it to have other brass issues. Any ammo you use in a big match should see your case gauge, factory or not!

Given how much money we spend on going to major matches, there’s not excuse to NOT to buy a case gauge in the appropriate caliber and drop check all match ammunition. You can drop check by feel in front of the TV, even!

I mentioned above that you could also for overall length under SAAMI spec, and for high primers while you’re gauging the ammo. I prefer to do both of these visually in 100 round ammo boxes. A round that’s overly long or short will visually stand out versus the other ammo in the box. When you look across the rounds at a shallow angle, with a light source behind the ammo (say, a window), you can see primer seating depth clearly. I find this to be more accurate than touch.

The case gauge you see in the pictures is a Dillon .38 Super stainless steel case gauge.

About the author


USPSA Grand Master, NRA Instructor, http://re-gun.com/about/

Permanent link to this article: http://re-gun.com/2011/04/a-case-for-the-gauge/

1 comment

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  1. Tim says:

    I just recently started reloading and quickly found out why I needed a case gauge. Since I have incorperated the gauge into my reloading routine I have yet to have any problems with case bulge. 

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