![]() It is a product of the Carpenter steel company, the sole maker, and you won't find it on the SAE list (although if you did it would probably be known as 3310). AR-15 bolts, for instance, are made of a steel known as Carpenter 158. When, and at what temperatures you add the alloying constituents also can change the final properties. However, the SAE standards are merely a list of ingredients. 30-06 hunting rifle already has a barrel that will shoot accurately for 5,000 rounds-which is like three lifetimes of hunting-who will pay twice the barrel cost for one that lasts 7,500 rounds? Most rifle makers realize that their customers won't pay the extra costs and find that 4140 is more than good enough. Army wants the extra wearability that 4150 offers and is willing to pay for it. That extra 0.1 percent makes the 4150 alloy so much harder that it becomes a lot more difficult to work with, but the U.S. The "big" difference between 41? The 4150 has 0.5 percent carbon in it. ![]() Mild steel, easy to machine and relatively inexpensive, works just fine. Something like a trigger guard doesn't have to be made of high-strength alloy steel. That leaves most of it, 94.25 percent, iron. It has about 1 percent chromium, 0.25 percent molybdenum, 0.4 percent carbon, 1 percent manganese, around 0.2 percent silicon and no more than 0.035 percent phosphorus and no more than 0.04 percent sulphur. Numbers such as 1060, 4140 or 5150 all designate how much of what is in them.Ĥ140, also known as ordnance steel, was one of the early high-alloy steels, used in 1920s' aircraft frames and automotive axles in addition to rifle barrels. The Society of Automotive Engineers uses a simple designating system, the four numbers you see bandied about in gun articles. Those alloying agents add useful things to the mix, such as easy machineability, corrosion resistance, abrasion resistance or tensile strength without brittleness to the steel grade in question. Steel can be alloyed with other metals such as nickel, chromium and tungsten-as well as non-metallic elements as molybdenum, sulfur and silicon. The crystals of steel are described by their sizes and shapes, and they have actual names such as austenite and martensite, cementite and ferrite. (Brief rant: Had I any hair left, I'd be pulling it out every time I heard of yet another lubricant that "gets into the pores of the steel.") The shape, size and alignment of those crystals determine the mechanical properties of the steel in question. Steel does not have pores it consists of crystals. What is steel? And why is it so important in gun building? Simply put, steel is iron with enough carbon in it to allow hardening-but not too much because that makes the resulting alloy brittle. If you're in the dark about what it all means, read on. Gun metal terms get bandied about in product literature and the firearms press as if everybody knew just what the hell they were talking about.
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