Converting an AR15 to .22LR, CMMG Conversion Kit
CMMG .22 LR Conversion Kit vs. Dedicated AR-15 Upper
Caleb from Brownells compares two approaches to shooting .22 LR with an AR-15: a conversion unit for a compatible .223 Remington or 5.56 NATO upper, and a dedicated rimfire upper.
Both offer a way to enjoy lower-cost practice and plinking. The difference comes down to initial expense, convenience, and the advantages of a barrel designed specifically for .22 LR.
Why Consider .22 LR?
Ammunition cost is the main reason Caleb introduces the conversion. Shooting rimfire can make a range session more affordable while retaining familiar AR-15 controls and handling.
There is also a straightforward benefit: shooting .22 LR is fun.
The Conversion Unit Option
Caleb first shows a CMMG conversion unit that works with a compatible centerfire upper. Its chamber adapter allows the rimfire system to use the existing barrel, paired with a dedicated .22 LR magazine.
This approach involves fewer additional components than a dedicated upper. It appeals to shooters who want an economical way to add rimfire capability to an existing setup.
Blowback Operation and Ammunition Considerations
The rimfire unit operates by blowback rather than using the upper’s centerfire gas system.
Caleb discusses fouling considerations when shooting .22 LR through a centerfire barrel and explains his preference for plated ammunition in that configuration. Ammunition choice and cleaning remain part of evaluating how the conversion fits a particular range routine.
The Dedicated .22 LR Upper
The second approach uses a barrel designed specifically for .22 LR and a matching rimfire bolt configuration. Caleb demonstrates this option with a Midwest Industries handguard and standard AR-15 upper receiver components.
The dedicated setup requires a greater initial investment, but it gives him a separate upper ready for rimfire use.
Why Caleb Prefers the Dedicated Barrel
Caleb favors the dedicated upper because its barrel is designed around .22 LR rather than accommodating rimfire ammunition through a centerfire chamber adapter.
He describes greater accuracy potential and fewer concerns about rimfire fouling affecting a centerfire gas system. This video explains those advantages without presenting a measured accuracy comparison between the two setups.
Rimfire-Specific Components
Caleb identifies the bolt unit and magazine as the key rimfire-specific components in the conversion approach. The dedicated setup also adds the purpose-built barrel and matching bolt interface.
He walks through the example upper’s assembly and discusses the tooling used along the way.
Convenience at the Range
For Caleb, carrying a dedicated .22 LR upper is worth the additional cost. It lets him keep a rimfire setup available alongside his centerfire upper.
The conversion unit remains the simpler investment, while the dedicated upper provides the configuration he prefers for regular use.
