Hey there, Squat Squad, and welcome back to Slav Guns. If you want to squeeze the most accuracy out of your rifle, you’re going to end up handloading. And once you start handloading for precision, one number matters before almost anything else: the maximum overall length for your specific chamber. Today’s quick take is on the tool I use to find it, the Hornady Overall Length (OAL) Gauge, in both the straight version for bolt actions and the curved version for semi-autos.
Quick note: this is a short “Quick Take” gear explainer I filmed at the bench in January 2021. It covers how the gauge works and why I use it. It is not a range test and evaluation, and there’s no shooting or accuracy testing in this one.
Find the gauges here: Hornady OAL Gauge (straight) and Hornady OAL Gauge (curved).
TL;DR
- What it does: Measures where a specific bullet touches the rifling in your chamber, so you know your max overall length for that bullet.
- Straight gauge: For bolt guns where you can pull the bolt and slide the whole gauge in.
- Curved gauge: Same idea, but curved at the bottom so it reaches into the chamber of a semi-auto.
- The catch: You need a Hornady modified (threaded) case for every caliber you load. Hornady makes them for pretty much everything, including newer stuff like 6mm ARC.
Why SAAMI numbers aren’t enough
Yes, there are SAAMI specifications for every cartridge. But every chamber reamer is going to be just slightly different. More importantly, every bullet is going to behave slightly differently. Some bullets want to be seated a little further back, so there’s more jump into the rifling. Other bullets like to be jammed right into the lands.
Whichever way your bullet likes it, all of that load development starts with one thing: knowing the maximum overall length for your chamber with that bullet. That’s where this gauge comes in handy.
How the Hornady OAL gauge works
The gauge itself is a metal body with a polymer insert, and it works together with Hornady’s modified cases. These are empty, unloaded pieces of brass that are threaded on the end. Here’s the process I walk through in the video:
- Thread the modified case onto the gauge until it’s flush.
- Drop the bullet you plan to load into the case mouth. The polymer rod is what pushes the bullet forward.
- Pull the rod back so the bullet sits somewhere in the case, lock it, and insert the gauge into your chamber.
- Slowly press the rod in until you feel the bullet engage the rifling. Lock it down right there.
- Extract the gauge. A lot of the time the bullet will actually stay stuck in the rifling. If that happens, take the gauge out without moving the lock, then knock the bullet out.
- Measure with your calipers from the bottom of the case to the bullet.
And voila: that’s your specific rifle’s maximum overall length for that cartridge and that particular bullet. Keep in mind the number will vary slightly depending on which bullet you’re using, so you repeat this for each bullet you load.
Straight vs. curved: bolt action or semi-auto
The straight gauge works perfectly with bolt-action rifles, where you can take the bolt out and put the entire gauge in from the back.
If you’re loading for a semi-automatic rifle, you can’t do that, so Hornady makes a curved gauge. It works exactly the same way, but it’s curved at the bottom so you can get it right into the chamber.
Modified cases: one per caliber
With either gauge, you’ll need to buy a modified case for every caliber you want to use it with. Hornady has them for pretty much every caliber out there, including newer ones like the 6mm ARC.
If you can’t buy one, or you can’t find one in stock, you can make your own by finding the right tap and drilling and tapping the bottom of a case. Doable, but for me the gauge plus factory modified cases has been a very worthwhile investment.
Bottom line
If you’re getting serious about precision handloading, the Hornady OAL gauge is one of those must-have tools. It takes the guesswork out of finding where your bullet meets the lands, and that’s the starting point for figuring out how much jump (or jam) your rifle actually likes. Straight for bolt guns, curved for semi-autos, and a modified case for each caliber.
Shooting one of the long-range cartridges I’ve covered? Check my Ruger Hawkeye Long Range Target 6.5 PRC review and Sierra at SHOT Show 2020 on 6.5 PRC and 300 PRC bullets.
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Keep squatting.
Do your bullets like a little jump or a hard jam into the lands? Drop it in the comments.
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