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Sturgeon's House

Baby's Rules For Lightweight Automatic Rifle Design


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As a current side project stops and starts according to my whims, I figured I might as well create here and keep updated a list of rules/guidelines for design of lightweight automatic/autoloading rifles and other weapons. Here's what I have so far:

1. Volume is mass; smaller means lighter.


2. The lightest, strongest shape is the sphere, and it has the least surface area for its volume. Cubes, though conceptually simple, should be avoided where possible. All light weapons desire to approach the shape of the cylinder, an elongate sphere.

3. (For conventional-layout weapons) Adding one ounce of weight in front of the point of balance adds two in total.

4. The primary mass is the primary driver of the total system mass. As a rule of thumb, adding 1 gram to the bolt mass adds 10 grams total to the rifle.

5. The only way to achieve exceptional lightness of weight is to reduce weight wherever possible, no matter how minor the savings in each case. The best way to lighten a rifle by 10% is not by cutting the weight of one component dramatically, but by reducing the weight of all components by 10%.

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I would ask what is the overriding purpose for the weapon? What is it designed for? Once you know that, then you know what to build. As opposed to the 16 pound monstrosities that you see on the range which are intended for 800-yard shots that can stop a bull elephant and then be used for suppressing fire, clearing rooms and a marital aid.

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Separation of function is a tricky one for light weight.


On the one hand, the AR-15 (and virtually every subsequent design) separates the function of providing a locking shoulder and containing the moving parts into the barrel extension and the receiver, while traditional designs had the receiver do both.  Profitably, this allows the AR-15 to use an aluminum receiver which clearly makes it lighter.


On the other hand, the insistence on making everything modular, separate pieces greatly adds to weight.

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