Understanding the Compatibility of .45 Auto Rim in .45 Colt and .45 ACP Revolvers and Single-Shot Rifles

The selection of ammunition is crucial for firearm enthusiasts and military personnel alike. One aspect that often confuses many is the compatibility of different types of cartridges, specifically the .45 Auto Rim and .45 ACP. This guide aims to clarify the differences between these two cartridges and their compatibility across various firearms.

Introduction to .45 Auto Rim and .45 ACP

When discussing the .45 Auto Rim and .45 ACP cartridges, it is essential to understand the fundamental differences between them. The .45 Auto Rim, developed by Peters Cartridge Company, is designed to work in revolvers and single-shot rifles. Unlike the .45 ACP, which is a rimless cartridge, the .45 Auto Rim has an extra thick rim, which is crucial for proper extractor function. This thicker rim allows for the extractor to engage and ensure proper case extraction.

The_background_of_Prodution_and_Use

During World War I, there was a significant demand for large-caliber sidearms. With the supply of 1911 45 ACP pistols being insufficient, manufacturers such as Colt and Smith Wesson (SW) received the task of converting their revolvers to chamber the same .45 ACP ammunition. This conversion involved modifying the revolver cylinders to accept half-moon clips, which held three rounds each, and allowed for a streamlined logistics of ammunition supply.

After the war, these converted revolvers were sold as surplus. Recognizing the need for civilian use, Peters Cartridge Company began producing the .45 Auto Rim. This cartridge was designed to fit into the SW and Colt 1917 models and in some gunsmith conversions of the SW Triple Lock and the Colt New Service.

Compatibility Across Firearms

It is important to note that the .45 Auto Rim cannot be used in firearms chambered for the .45 Colt. This is because the .45 Colt has a standard rimmed design that is significantly thicker than the .45 Auto Rim. For this reason, the .45 Auto Rim cannot fit in a .45 Colt chamber, as it would not seat properly and could lead to catastrophic failures.

On the other hand, the .45 ACP is a rimless cartridge, meaning it does not have a thick rim. This allows the cartridge to function properly in modern revolvers, such as the Smith Wesson Model 25 or Governor. However, the .45 Auto Rim's thick rim prevents it from being used in these modern firearms.

A Special Case: The SW 25 and 625

There are some exceptions to the general rule. Smith Wesson's Model 25 and 625 revolvers, while chambered in .45 Auto/45 Auto Rim, can accommodate both the .45 Auto Rim and .45 ACP. This is due to the SW Model 25's unique design that allows for interchangeable cylinder inserts, which can be switched to either the standard .45 Auto Rim or the .45 ACP design.

The SW 625, on the other hand, is a single-action revolver, and it too can use both types of cartridges. This versatility is due to the gun's design allowing for the thick rim of the .45 Auto Rim to be properly engaged by the extractor.

Additional Modern Cartridge: The 45 Cowboy

In recent times, a new cartridge has emerged that combines the best features of the .45 Colt and .45 ACP, known as the 45 Cowboy. This cartridge is tailored for cowboy action shooters and is characterized by its smaller case capacity, offering more consistent ballistic performance and the ability to fit more cartridges in the magazine tube of lever rifles. Additionally, the 45 Cowboy can be easily adapted to short stroke modifications, making it a versatile choice for these shooters.

Conclusion

In conclusion, the .45 Auto Rim and .45 ACP have distinct characteristics that make them compatible or incompatible with different firearms. While the .45 Auto Rim is designed to work in older revolvers like the SW 25 and 625, it is not compatible with .45 Colt and many modern .45 ACP revolvers. Conversely, the .45 ACP is more versatile and works in a wide range of firearms, but it lacks the thick rim necessary for the .45 Auto Rim's proper function. Lastly, the 45 Cowboy, a modern take, offers a balanced design for specialized applications.