For years, if you wanted an AR-15 that shot rimfire ammunition, your options started and stopped with .22 LR. It was cheap, it was fun, and it was great for training — but it never felt like a true step up from your centerfire build. That's changing. Rimfire AR-15 platforms are now being offered in .22 WMR (Winchester Magnum Rimfire) and .17 HMR (Hornady Magnum Rimfire), and the shift is a bigger deal than it might sound at first.

Why This Matters for AR-15 Shooters

The AR-15 platform has always been prized for its modularity. Swap an upper, change a caliber, keep the same lower and furniture you're already comfortable with. Rimfire uppers extended that flexibility to low-cost plinking and practice, but .22 LR has real limits: modest range, a rainbow-like trajectory past 75-100 yards, and not as much punch for small game or pest control.

.22 WMR and .17 HMR close that gap. Both cartridges were originally built for bolt-action rifles and revolvers, prized by varmint hunters for flatter trajectories and more authority at distance. Bringing them into an AR-15 upper means shooters can now get magnum-rimfire performance with the ergonomics, optics compatibility, and familiar manual of arms of the AR platform.

.22 WMR vs. .17 HMR: What's the Difference?

If you're deciding between the two chamberings, it helps to know what each one is actually good at.

.22 WMR (.22 Magnum)

• Fires a heavier bullet than .22 LR, typically 30-50 grains
• Muzzle velocities generally in the 1,800-2,200 fps range depending on load and barrel length
• Retains energy well at moderate range, making it a solid choice for small game, predator control, and home-defense-adjacent applications where more terminal performance is wanted
• Slightly more felt recoil than .17 HMR, but still very mild by centerfire standards

.17 HMR

• A .17-caliber bullet (typically 17-20 grains) built on a necked-down .22 WMR case
• Blistering velocities, often exceeding 2,500 fps
• Extremely flat trajectory, which makes it a favorite for varmint hunters shooting at extended rimfire ranges
• Less bullet weight means less wind resistance to fight, but also less penetration on larger animals

Neither cartridge replaces .22 LR for high-volume, low-cost practice. Instead, they give AR-15 owners a second and third rimfire option purpose-built for hunting and precision work rather than pure plinking.

What an AR-15 in .22 WMR or .17 HMR Is Good For

• Varmint and predator hunting — flatter trajectories and more downrange energy than .22 LR
• Backyard and rural pest control — more effective on the vermin .22 LR sometimes just doesn't put down cleanly
• Low-recoil training that still teaches real ballistics — because the drop and wind drift behave more like a true hunting round than .22 LR does
• A second rimfire upper for AR-15 owners who already run a .22 LR conversion and want more range and knockdown power without stepping up to a centerfire caliber

What to Know Before You Buy

A few practical points matter more with rimfire AR uppers than with a typical .22 LR swap:

1. Magazines are largely caliber-specific. In most cases, you'll need dedicated magazines for your rimfire AR upper, and you generally can't share mags with a standard .22 LR rimfire upper. That said, because .22 WMR and .17 HMR share the same case dimensions, some magazines — like BlackDog's AR-15 rimfire mags — are dual-rated and can run either cartridge, so it's worth checking whether your chosen upper supports a shared magazine before buying separate ones.
2. Bolt and feed geometry differ from .22 LR. These are purpose-built uppers, not simple bolt swaps, so make sure you're buying a complete, matched upper rather than trying to mix and match parts.
3. Ammunition cost is higher than .22 LR. Both .22 WMR and .17 HMR cost meaningfully more per round, so budget accordingly if you're planning high-volume range sessions.
4. Barrel length and twist rate affect velocity and accuracy. As with any rimfire cartridge, shorter AR-length barrels will give up some velocity compared to a dedicated bolt-action hunting rifle, so check manufacturer specs against your intended use.
5. Check state and local regulations. Rules around magazine capacity, barrel length, and overall configuration can vary, so confirm your build is compliant wherever you live.

The Bottom Line

Rimfire AR-15s in .22 WMR and .17 HMR aren't just a novelty — they fill a real gap between economical .22 LR training and full centerfire hunting rifles. For AR-15 owners who want more reach, flatter trajectories, and genuine field performance without stepping up to a centerfire caliber, these new chamberings are worth a serious look. Whether you're after a dedicated varmint upper or just want to expand what your AR-15 can do, .22 WMR and .17 HMR give you options that simply weren't available on this platform before.