Disclaimer: The following is provided for informational purposes only. The information here is derived from open sources. In the U.S. there is nothing inherently illegal or controlled about this information. This document discusses general principles and not specific construction details. It is not intended to be a construction guide, but an overview of general concepts. Do not attempt to construct firearms even if you are a) a skilled machinist, b) thoroughly familiar with all relevant engineering issues such as strength of materials, heat treatment, metal finishes and corrosion, c) capable of stress, strain and failure analyses, d) fully competent in developmental safety issues, etc. By proceeding you agree that you are completely responsible for your actions. If you do not agree, do not proceed further.


This document provides a descriptive outline of the principles of automatic and semi-automatic firearms. It's derived mainly from Principles of Firearms by Charles Balleisen, a relatively brief engineering book published towards the end of World War II in 1945 by John Wiley and Sons of New York and Chapman and Hall Limited of London. Then a Major in the US Army Ordnance Department, Balleisen applied mechanical engineering principles to analyze firearms designs through the end of the war. Balleisen sought to educate his wartime audience towards a sound, well-versed engineering approach to arms design. Based on open literature of the time he included work from French, German and U.S. sources. He also included analyses of a few key contemporary arms. His book is likely long out of print. I found a copy in my university's engineering library.

Due to typesetting complexity I have not included Balliesen's formulas and sample calculations in this document. Since his work is no longer available I may attempt to rectify this later. Until then for a formal treatment of this subject, including background, theory and formulas, please see the recent (1997) Brassey's Essential Guide to Military Small Arms: Design Principles and Operating Methods. It is of similar scope to Balliesen's work, but is broadened to include a greater variety of designs, particularly those from slavic countries, and more detailed analyses. This Brassey's title is available at amazon.com and also at Barnes and Noble. I've just received and begun to review my copy. From this early sampling, I can strongly recommend it to any student of small arms design.

There are many types of firearms, from muzzle-loading muskets, through bolt-action rifles, to magazine-fed semiautomatic rifles, to belt-fed machine guns, slide-action shotguns, revolvers, pistols, etc. At their inception almost all were designed as state of the art military weapons. While hunting and recreational uses of firearms are popular, most common small arms designs were originally military designs and many continue to have military use.

Since bolt-action rifles, revolvers, slide (pump) action shotguns, and so forth operate on different principles from automatic and semiautomatic firearms, they are not included in this discussion. However, many of the basic functions and issues other than the operating system are similar or identical across all firearms.

Note that this document does not attempt to catalog all instances of firearms. Such titles can be found in the Bibliography. Rather the goal is to describe the fundamental definitions, functions and operating principles of automatic and semi-automatic firearms. In order to do so a few key examples of existing arms are examined throughout the document. Some of the history surrounding their development is also discussed.

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