One source of variation in rimfire ammunition is rim thickness. In this video, we’ll show how to measure it using a Hornady Lock-N-Load 17-22 Rim Thickness Gauge. 

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Background

Rimfire isn’t just fun, but presents unique challenges. As with any caliber, I love doing everything possible to shrink my groups and hit crazy targets. In example, hitting a steel target at 511 yards with a .22 LR. 

When it comes to rimfire, I generally sight in at 50 yards and progress to 100 then 200 yards. I like to see how the groups vary across distance. 

It’s also important to realize that rimfire varies significantly from lot to lot.

Certain lots will perform better in some rifles than in others. This is why locations like the Lapua Test Center exist, to allow shooters to find the best lot for them.

While we’ve long been aware of this at Ultimate Reloader, one thing we haven’t taken a close look at is measuring rim thickness.

About the Hornady Lock-N-Load Rimfire Thickness Gauge

The Hornady Lock-N-Load Rimfire Thickness Gauge is extremely easy to set up.

Simply screw both the body and anvil to the calipers. Hornady recommends using the anvil on the traveling blade, but Kyle prefers the opposite.

When the body, anvil, and bushing are secure, make sure there are no gaps and zero out the calipers. 

Drop a round into the gauge and record the value! 

This tool comes with a lanyard to prevent droppage. We secured it in a vise during use for the same purpose. The reason this matters is that a hard drop while measuring ammunition can set a round off. 

From Hornady: 

Sorting ammo by rim thickness will provide ammo with similar ignition qualities for improved accuracy.

This proven technique is used by competitive shooters and varmint hunters.

The rimfire gauge attaches to your caliper and includes bushings for use with most (not compatible with 17 WSM) .17 and .22 caliber rimfire ammo.

What’s in the Box

Included in the kit is a lanyard, two bushings (.17HMR and .22 Mag), anvil, body, and some screws. This tool does not come with a set of calipers – install it on your calipers of choice.  

Measurements

Kyle measured the rim thicknesses of 20 rounds for five types of ammunition: Remington Golden Bullet, Lapua Super Long Range, Lapua Center-X, RWS R50, and Federal Game-Shok. 

The average rim thickness across all five types of ammunition tested ranged from 0.03805” to 0.039575”.

Remember that human error is still a factor while using calipers. Also take the capabilities of your calipers into account. With such small numbers, we are on the cusp of measurement error. 

The standard deviation results surprised us. Federal Game-Shok was the most consistent, followed by Lapua Center-X and RWS R50.

Remington Golden Bullet had the most variation. These are not known for their accuracy, but affordability, so this was not surprising. Kyle’s research indicated that rim thickness itself isn’t as critical as the consistency of it, but the question remains, does it matter?  If you have thoughts on this topic, please drop them in the comments! 

Conclusion

I was surprised at how close the rimfire thickness was across all rounds tested, with the exception of Remington Golden Bullet. While we didn’t come to any conclusions on the true effects of rim thickness variation, it’s still an interesting experiment. 

Get the Gear

Hornady Rimfire Thickness Gauge at Midsouth Shooters Supply

.22 LR Ammunition at Midsouth Shooters Supply

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Thanks,
Gavin Gear