Title: 5 Best Rimfire Cartridges for Customizing Your AR-15 Platform in 2026

Meta Description: Discover the top rimfire cartridges for AR-15 customization. From affordable .22LR uppers to high-velocity .17 HMR and .22 WMR builds, learn which rimfire options deliver fun, accuracy, and low-cost plinking on your AR-15 platform. Perfect for trainers, varmint hunters, and custom builders.

Introduction

The AR-15 platform is incredibly versatile, and swapping to a rimfire cartridge is one of the smartest customizations you can make. Whether you're looking to save money on ammo, train new shooters, or enjoy quiet plinking sessions, rimfire conversions or dedicated uppers transform your AR into an affordable, low-recoil rifle.

Rimfire options shine for their low cost per round (especially .22LR), minimal recoil, and excellent accuracy at shorter ranges. In this guide, we'll cover the favorite rimfire cartridges for AR-15 builds, their pros/cons, and tips for customization.

Primary keywords: rimfire AR-15, best .22LR upper, AR-15 rimfire conversion Long-tail targets: best rimfire cartridge for AR-15, .22LR vs .17 HMR AR build, customize AR-15 with rimfire

Why Customize Your AR-15 with Rimfire?

• Cost savings: .22LR ammo is often under $0.05 per round vs. $0.30+ for 5.56.
• Training tool: Practice marksmanship, transitions, and drills without developing a flinch.
• Fun factor: Low noise and recoil make it ideal for range days and introducing beginners.
• Varmint/small game capability: Some options reach out further with flatter trajectories.
• Easy swap: Dedicated uppers from brands like PSA, CMMG, JP Enterprises, and Bear Creek Arsenal drop right onto standard AR-15 lowers.

Top 5 Favorite Rimfire Cartridges for AR-15 Platforms

1. .22 Long Rifle (.22LR) – The King of Rimfire AR Builds

.22LR is by far the most popular and practical choice for AR-15 customization.

Pros:

• Extremely affordable and widely available.
• Dedicated uppers are reliable and accurate (1-1.5 MOA possible with match ammo).
• Low recoil, quiet with suppressors.
• Huge aftermarket support (PSA, CMMG, BoreBuddy, JP SuperMatch).

Cons:

• Limited effective range (best under 100-150 yards).
• Can be finicky with cheap ammo in some uppers.

Best for: Plinking, training, small game, and high-volume shooting. Most shooters start here.

Customization tips: Look for 1:16 twist barrels. Popular lengths: 16" for balance, 10.5-12" for pistols/SBRs.

2. .17 Hornady Magnum Rimfire (.17 HMR)

.17 HMR brings serious velocity and a flat trajectory to the AR platform.

Pros:

• ~2,500 fps muzzle velocity — much flatter shooting than .22LR.
• Excellent accuracy for varmint hunting out to 150-200+ yards.
• Devastating on small game with explosive expansion.

Cons:

• More expensive ammo than .22LR.
• Fewer dedicated uppers available (requires specific barrels).
• Sensitive to wind due to light bullets.

Best for: Precision varmint control and longer-range rimfire fun.

3. .22 Winchester Magnum Rimfire (.22 WMR / .22 Mag)

A step up in power from .22LR with better terminal performance.

Pros:

• Heavier bullets (40gr) deliver more energy and penetration.
• Good for small-to-medium game and longer ranges than .22LR.
• Fun alternative when you want more "thump."

Cons:

• Not as accurate as .17 HMR at distance.
• Ammo cost between .22LR and .17 HMR.

Best for: Hunters who want a rimfire that hits harder.

4. .17 Mach 2

A milder, more affordable alternative to .17 HMR.

Pros:

• Uses .22LR cases necked down — cheaper and more available ammo.
• Low recoil with decent speed.

Cons:

• Less popular, so fewer AR-specific components.
• Lower velocity than .17 HMR.

Best for: Budget shooters wanting .17 caliber performance.

5. Other Niche Options (.22 Short, .17 Winchester Super Magnum)

These are rarer but great for specialized builds. .17 WSM offers even higher velocity for serious varmint work.

Customization Guide: Building Your Rimfire AR-15

1. Dedicated Upper vs. Conversion Kit — Dedicated uppers are more reliable long-term. Conversions (like CMMG .22LR bolt) are cheaper but can have feeding issues.
2. Key Components:
   • Barrel: Match-grade with proper twist rate.
   • Bolt: Rimfire-specific (different extractor/ejector).
   • Magazines: Dedicated .22LR mags or adapters.
   • Optics: Red dot or low-power variable (LPVO) for fast target acquisition.
3. Popular Brands (2026): PSA, Right To Bear, Bear Creek Arsenal, JP Rifles, Ghost Rifles.
4. Suppressor-Ready: Most rimfire builds pair perfectly with .22 cans for backyard-friendly shooting.

Which Rimfire Cartridge Should You Choose?

• Budget/High Volume: .22LR
• Varmint Hunter: .17 HMR
• Balance of Power: .22 WMR

Many builders own multiple uppers and swap them based on the day's mission.

Conclusion

Customizing your AR-15 with a rimfire cartridge is one of the most rewarding and practical upgrades available. It extends your range time, sharpens your skills, and adds versatility without breaking the bank. Start with a quality .22LR dedicated upper and expand from there.

What’s your favorite rimfire AR build? Drop a comment below with your setup!