Modern firearms utilize cartridges, which are a single unit of ammunition that combine a bullet, a propellant, and a primer within a cartridge case. The primer is a small charge of an impact-sensitive chemical mixture. The method of ignition of the primer is used to describe the type of cartridge. Rimfire ammunition locates the primer inside a rim, and centerfire ammunition locates the primer at the center of the case head. Generally, centerfire rifle cartridges are more powerful than rimfire cartridges, but centerfire rifle cartridges are significantly more expensive to purchase than rimfire cartridges. Rimfire firearms are also subjected to fewer legal restrictions in many jurisdictions relative to centerfire firearms.
Typically, semi-automatic rifles allow the shooter to shoot only the caliber of bullet and the type of cartridge the rifle is sized to receive. However, it is often desirable for shooters to be able to practice shooting with less powerful and/or less expensive ammunition. Lower power rimfire ammunition allows a shooter to become familiar with the feel of the firearm while shooting a round that has less recoil and is considerably cheaper than centerfire ammunition. In addition, the reduced power of the rimfire ammunition allows it to be shot at smaller range facilities. For example, many shooting ranges, particularly indoor ranges, which explicitly prohibit the use of centerfire rifles allow the use of rimfire rifles. However, accommodating a rimfire cartridge in a semi-automatic rifle designed to receive a centerfire cartridge creates a challenge to retaining the rifle's original fire control group and lower receiver because the firing pin must strike the rim of the cartridge rather than the center.
Therefore, a need exists for a new and improved semi-automatic rimfire rifle that converts a semi-automatic rifle from a centerfire caliber to a rimfire caliber while retaining the rifle's original fire control group and lower receiver. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the semi-automatic rimfire rifle according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of providing a semi-automatic rimfire rifle that converts a semi-automatic rifle from a centerfire caliber to a rimfire caliber while retaining the rifle's original fire control group and lower receiver.