As a kid I had heard of “erosive” primers in .22 rimfire cartridges. I was under the (evidently correct) impression that it referred to the practice of putting ground glass in the priming compound, but thought it was a practice that had been discontinued long ago. But I just saw a video about cleaning 22 Long Rifle barrels produced by the Eley ammunition company, and the narrator mentioned pushing out the ground glass—which was a surprise.

Therefore my question to Gemini AI:
“Does 22 Long Rifle ammunition have ground glass in the primer?”

(I know a lot about guns, but I’m always learning something new. Did it surprise you as well, or was it “Oh yeah; everyone knows that”? Both Gemini and generic Google AI said basically the same things. As is often true, Copilot is too squeamish to respond.)

Answer below.
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Yes, most .22 Long Rifle (.22 LR) ammunition does contain ground glass (often referred to as a "frictionator") in the priming compound.

While it might seem counterintuitive to put an abrasive material in a firearm, it serves a critical mechanical purpose specifically for rimfire cartridges.

Why Ground Glass is Used

In a centerfire cartridge (like a 9mm or .308), the primer cup contains a small metal piece called an anvil. When the firing pin strikes the primer, it crushes the explosive compound against that anvil to trigger the explosion.

Rimfire cartridges, however, do not have an internal anvil. Instead: The priming compound is spun into the hollow rim of the case. When the firing pin hits the rim, it crushes the compound against the brass case itself.

Because this "crush" is often less efficient than a centerfire strike, ground glass is added to the mix. The sharp edges of the glass create the necessary friction to ensure the lead styphnate (the primary explosive) ignites reliably every time the trigger is pulled.

Key Considerations

Manufacturer Differences: Most major American manufacturers (CCI, Federal, Winchester) use ground glass. Some high-end European match ammunition, such as Eley, uses a different patented process (Eleyprime) that achieves ignition without traditional ground glass to minimize barrel wear and improve consistency.

Barrel Wear: Because .22 LR operates at low pressures and the bullets are usually lead or copper-washed, the "glass dust" left behind is generally pushed out by the next shot. While it is technically abrasive, most .22 LR barrels can fire tens of thousands of rounds without significant accuracy loss from the glass.

Cleaning: The residue from the glass and lead styphnate is one reason .22 LR is considered "dirty" compared to centerfire rounds. This residue can accumulate in the action and the bore, making regular cleaning important to maintain reliable cycling in semi-automatics.

Lapua and SK (both owned by the Nammo Group) generally do not use ground glass in their priming compounds. Instead, they follow the European match-grade manufacturing tradition, which relies on chemical sensitizers rather than mechanical frictionators like glass.

### The European Approach: "Glass-Free"
While most high-volume American manufacturers (CCI, Federal, Winchester) use ground glass to ensure ignition in rimfire cases, premium European brands like **Lapua**, **SK**, **RWS**, and **Eley** use different formulations:

* **Lapua and SK:** These brands use a lead-styphnate-based priming compound that is chemically sensitive enough to ignite without the need for an abrasive frictionator. This is why their residue is often described as "sooty" or "greasy" rather than "gritty."
* **The Eley Factor:** Eley is the most famous for this with their patented **Eleyprime** system. While Lapua and SK use their own proprietary mixtures (often manufactured in Germany or Finland), they share the same design philosophy: protecting the high-precision barrels of target rifles from the micro-abrasions caused by glass dust.

### Why It Matters for Your Barrel
Because Lapua and SK omit the ground glass, they offer two distinct advantages for precision shooting:

1. **Reduced Bore Wear:** In a match-grade barrel, even microscopic wear can affect accuracy over tens of thousands of rounds. Without glass dust acting as a "lapping compound" with every shot, these barrels tend to maintain their "match" accuracy for a much longer lifespan.

2. **Lubrication Synergy:** You’ll notice that Lapua and SK bullets are famously "greasy" or "oily" compared to the dry wax on American ammo. This lubricant is specifically formulated to work with their chemical residue. Switching back and forth between "glass" ammo (like CCI) and "glass-free" ammo (like SK) often requires a thorough cleaning of the bore, as the glass dust from the cheaper ammo can "chew up" the soft oily seasoning left by the match ammo, leading to a temporary loss in accuracy.

> **Note:** If you are shooting SK Standard Plus or Lapua Center-X, you are essentially shooting a "cleaner" ignition system that is designed to be as gentle on your rifling as possible.

In view of the intense interest that this thread has generated already ( ), I’ll add that one Internet response mentioned that priming compounds without the glass were less likely to form a hard carbon ring forward of the chamber. Cleaning and removing such rings is something that gets a lot of video discussion. I suppose I should get unlazy and check my own rifles.

Thank you for posting this. I was not aware of the use of ground glass and I do find it interesting. I do not shoot enough .22 to be worried about the barrel wear, and I don’t own a “precision” .22, so I guess it’s all academic for me.

"You learn something new everyday".
Thanks for the info.

quote:

Originally posted by sigfreund:
In view of the intense interest that this thread has generated already, I’ll add that one Internet response mentioned that priming compounds without the glass were less likely to form a hard carbon ring forward of the chamber.

That's interesting if true. I'd never hear of it before, or of ground glass in the priming compound for that matter. I have one .22 that's not a "precision" anything, just a semi-auto pistol. After a few hundred rounds it suddenly started keyholing. Bad. I found, not a ring, but a ridge of hardened gunk just in front of the chamber. Took a lot of solvent and elbow grease to clean it out, but the keyholing stopped then. I assumed there was a machining flaw in the barrel that was grabbing gunk as it flew by, but maybe not.

Very interesting. That explains why the SK ammo I use for long range .22 shooting feels slick.

I was unaware of the glass in a lot of .22 rounds. Very informative. Thanks for sharing.

Glass dust has been put into priming compounds for decades to ensure reliable ignition via friction. This goes for rimfire primer as well as centerfire. It sounds odd at first, but a firing pin impacting a percussion primer is an impact AND friction event because of the pinching motion between the primer cup and anvil, or rim pinching in a rimfire.

Other additives to sensitize primer compositions include tetrazene (a sensitive primary explosive) and antimony trisulfide, which is used as a fuel (in concert with a non-hygroscopic oxidizer like barium nitrate) and is pointy, jagged, or needle-like, which helps increase friction sensitivity of a mixture. The fact that it also has a high melting point relative to other constituents in the mixture helps with this effect, also. The same for glass dust, obviously.

I'm not worried about either doing any wear/tear to my firearms. The reliability of the primers trumps any of that.

quote:

Originally posted by flesheatingvirus:
as well as centerfire.

Not according to what I found.
Do you have any links to what supports that?

This message has been edited. Last edited by: sigfreund,

You won't find manufacturers posting their primer composition recipes, but you can find things piece-wise. I also didn't mean to allude that it's in ALL of them. It has also been more traditionally used in rimfire than centerfire. Glass isn't always the best option. While it friction sensitizes, it's also a diluent because it doesn't participate in any energetic reactions. Here's a patent that mentions it. Like I said, piece-wise. You'll see it more in a more prominent role in some "non-toxic" primer mixes. Other friction sensitizers, like the antimony trisulfide I mentioned, are toxic, but glass is not.

https://patents.google.com/patent/US8454770B1/en

I've also had to download/analyze percussion primers at work; the results of testing some, but not all, compositions did show some silica.

Thanks.

No problem. I wish I could point to detailed SDSs from Winchester or other makers, but secret sauce and all that. Overall I have zero concern about glass dust being in my primers.

1. The amount is a tiny fraction of the overall primer composition, if it's there at all. Recall what its roles are- a sensitizer and a diluent. You don't need much sensitizer in most energetic mixtures to see the effect. Any more and it degrades the output of the mixture, though I have seen diluents use that way on purpose, too.
2. The wear at the throat for higher pressure rounds due to the hot gases jetting around the base of the bullet as it exits the case will have a significantly larger effect on barrel life.
3. Same as above, but for the actual bullet going down the bore and contacting the rifling. I would think #2 is waay more of a factor, though.

Based on countless sources and discussions, there is no question in my mind that centerfire throat erosion and general barrel wear is dependent almost exclusively on factors relating to charge volume and caliber (diameter). That’s confirmed by the simple fact of how often competition shooters’ rifle barrels must be replaced to keep an acceptable level of precision. If glass in the primers were the issue, then all barrels would last about the same number of rounds, and that’s obviously not true.

Neither of the centerfire factors is very significant in 22 Long Rifle shooting, though, and therefore it makes absolute sense to me for the Internet claim to be correct that barrel wear and possibly the development of hard carbon rings can vary whether rimfire priming contains glass.

Long, long ago my father told me of “shooting out” the barrel of a 22LR rifle in his youth. Although I never knew the details of the gun involved, it would have been one that was made no later than the late 1920s when, I strongly suspect, the steel in a cheap rifle of the sort he would have owned was very likely of lower quality than that of almost any 22LR rifle made today. As I mentioned earlier, I specifically recall seeing boxes of the ammunition labeled as “non-erosive,” which I’m pretty sure referred to the claim that it didn’t contain some sort of harmful “frictionator” to enhance ignition reliability. Although I’m leery of accepting some Internet claims, it seems plausible that references to other materials besides ground glass being used for the purpose are correct, and some could have been very “erosive,” such as actual fine sand.

In any event, it also seems plausible that competitors who fire very high volumes of 22LR ammunition with very expensive rifles would prefer ammunition that avoids glass entirely or limits its use as much as possible. I have shot about 6200 rounds with my Tikka T1x in the space of about 10 months and I consider that to be a lot, but (again, according to the Internet), some shooters fire that many or more in a single month.

Anyway, a firearms-related discussion on a firearms-related forum, and therefore possibly of interest to some members. And thanks again for your comments.